Gis

On

Geographic Information System Course No.: GEO 411

Submitted To:

Submitted By:

Md. Iqbal Sarwar

Exam. Roll No.: 2006/81 Reg. No.: 3414 Session: 2005– 06 Year: 4th Year

Assistant Professor

Department of Geography and Environmental Studies, University of Chittagong.

Date of Submission: 07.06.2

2

CHAPTER ONE 1.1

Introduction:

The concept of geographic information systems (GIS) is not new. It was first applied conceptually when maps on the same topic made on different dates were viewed together to identify changes. Similarly, when maps showing different kinds of information for the same area were overlaid to determine relationships, the concept of GIS was actually in use. What is new and progressing rapidly is advancing computer technology, which allows the low-cost examination of large areas frequently, and with an increasing amount of data. Digitization, manipulation of information, interpretation, and map reproduction are all steps in generating a GIS that now can be achieved rapidly, almost in real time. The concept of a GIS is basically analogous to a very large panel made up of similarly shaped open boxes, with each box representing a specified area on the earth's surface. As each element of information about a particular attribute (soil, rainfall, population) that applies to the area is identified, it can be placed into the corresponding box. Since there is theoretically no limit to the amount of information that can be entered into each box, very large volumes of data can be compiled in an orderly manner. There are many kinds of GIS, some more suitable for integrated development planning studies and natural hazard management than others. At the most elementary level, there are simple manual overlay techniques, such as the one proposed by McHarg in Design with Nature, which have proven to be very valuable tools. However, the information needed for hazard management and development planning can become so overwhelming that it is almost impossible to cope with it manually. At the other extreme are highly sophisticated computerized systems that can analyze baseline scientific data such as satellite imagery and can produce, by using plotters, large-scale maps of excellent cartographic quality. Such systems are very expensive, difficult to operate, and may exceed the needs of many planning offices. 1.2 Definition of GIS: A geographic information system is a system designed to capture, store, manipulate, analyze, manage, 3

and present all types of geographical data. The acronym GIS is sometimes used for geographical information science or geospatial information studies to refer to the academic discipline or career of working with geographic information systems.[1] In the simplest terms, GIS is the merging of cartography, statistical analysis, and database technology. A GIS can be thought of as a system—it digitally creates and "manipulates" spatial areas that may be jurisdictional, purpose, or application-oriented. Generally, a GIS is custom-designed for an organization. Hence, a GIS developed for an application, jurisdiction, enterprise, or purpose may not be necessarily interoperable or compatible with a GIS that has been developed for some other application, jurisdiction, enterprise, or purpose……………..Wikipedia .  According to Arnoff(1989), “A computer based system

that

provides

four

sets

of

capabilities

to

handle

georeferenced data: data input , data management (data storage and retrieval ),manipulation and analysis and data output.”  According to

D.W. Rhind (1989) ,“GIS is ‘a computer

system that can hold and use data describing places on the Earth’s surface”  According to Peter A.Burrogh (1986),“A set of tolls for

collecting, storing, retrieving at will, transforming and displaying spatial data from the real world for a particular set of purposes.”  According to Department of the Environment (1987) ,

“A system for capturing, storing, checking, integrating, manipulating, analyzing and displaying data which are spatially referenced to the Earth; fall into this category. ’’  According to ESRI, “An organized collection of computer

hardware, software, geographic data & personnel designed 4

to efficiency capture, store, update, manipulated, analyze, &

display

all

forms

of

geographically

referenced

information.” 

“GIS is defined as an information system that is used to it store.

Retrieve,

manipulate,

analyze

and

output

geographically referenced data or geospatial data, in order to support decision making for planning and management of land use, natural resources, environment, transportation, urban facilities, and other administrative records.” Goodchild (1987) offers a useful summary of key GIS. ➠

Geographical information is information about places on the Earth’s surface.

➠

Geographical

information

technologies

include

global

positioning system (GPS), remote sensing and geographical information systems. ➠

Geographical information systems are both computer system and software.

➠

GIS can have many different manifestations.

➠

GIS is used for a great variety of applications.

Geographical information Science is the science behind GIS technology. 1.3 History and Development of GIS: In the London City Cholera was spread out in 1854. Soho a British researcher noticed that, cholera is more spread in some water pump area. From this Soho confirm that, cholera spread from some polluted water pump. Then he showed by the map through the collection of information about the disease & the affected

5

people. As a result the problem can be identified & necessary steps has been taken. This work gets praised in London. In the following shows in the amp the location of water pump & the amount of cholera death. Most of the GIS scientist think about Soho’s spatial & non-spatial data presentation is introduction of

6

GIS.

7

Fig.1. E. W. Gilbert's version (1958) of John Snow's 1855 map of the Soho cholera outbreak showing the clusters of cholera cases in the London epidemic of 1854. ………………Wikipedia. GIS and map analysis developments began around the same time as related developments in computer cartography and spatial statistics. They were promoted by the limitations of hard-copy maps, problems with overlaying data sets and the increasing size and number of available data sets (Tomlinson, 1988). The initial development (in the 1960’s) were technical and were aimed at developing a set of spatial data handling and analysis tools that could be used with geographical database for repeated problem solving (Tomlinson, 1988). One of the first systems called GIS appeared in Canada in 1964. Godchild (1995) considers that the roots of current GIS lie in the 1960s, and then pioneering work by the US Bureau of Census that lead to the digital input of in 1970 Census. In turn, these developments influenced work at the Harvard Graphics Laboratory, which led directly to the production of some of the first commercial GIS software, including the package ARC/INFO. 1.3.1 CGIS: AS Early GIS. The Canadian Geographic Information System (CGIS) used data collected for the Land Inventory System and was developed as a result of the requirements of the Canadian Agriculture and Development Act. It was designed to produce maps of the crops

8

that areas of land were capable of producing and to map land capability for forestry (based on soil, climate, drainage and physical land characteristics). Over the years CGIS has been modified and improved to keep pace with technology and the equipments are now. For example, microcomputers are now used for data input analysis. However, the overall components of CGIS have remained constant. There is a subsystem for scanning input and raster editing that allows editing and verification of scanned images and some autoprocessing.

Additional

subsystems

include

the

interactive

digitizing and editing subsystem and a cartographic output subsystem.

1.3.2 The Development of ESRI: Yea

Development of ESRI.

rs 196

ESRI founded by Jack and Laure Dangermond as a

9 197

privately held consulting group in Redlands, California. ESRI is involved in applications such as site selection

0

and urban planning which lead to the development of

198

many of the technical and applied aspects of GIS. ARC/INFO GIS for minicomputer launched. Later the

1

product is shifted to UNIX workstations and PCs the

199

ESRI user conference attracts 18 participants. ARCVIEW is launched (desktop mapping and GIS tool)

1 199

SDE

(a

client-server

product

9

for

spatial

data

5

management) and business map (a consumer mapping

199

product) are launched. Arc Data online (Internet mapping and data site)

8 199

launched. Arc Info 8 release. Arc News circulation exceeds

9 200

200000. Geography network for publishing, sharing and using

0 200

geographic information on the Internet launched. ESRI celebrates 32 years providing software and

1 services to the GIS industry Source: Adapted from ESRI, 2001

1.4 The Stage of GIS Development: Stage

and Descripti

Date

on Pioneering

Characteristics ➠

1. Early 1960s -

Experimen 2. 1973 – early t

3. 1982 – late 1980s 4. 1990s

personalities

important.

1975

1980s

Individual

➠

Mainframe-based

➠

dominant. Local experimentation

and

Practice

systems and

action. ➠

GIS

Commercia

➠

agencies. Increasing range of vendors.

l

➠

Workstation

dominance User

➠

becoming available Embryonic standardizations.

dominance

➠

Systems

10

fostered

and

by

PC

available

national

systems

for

all

,

Vendor

competitio

hardware platforms. ➠

Internet mapping launched.

n Sources: adapted from Tomlinson, 1990; Coppock and Rhind, 1991.

1.5 GIS and Bangladesh: In Bangladesh there is a growing application of GIS in land inventories, the population census, urban planning, forestry, petroleum and gas exploration industries, utilities, transportation systems and so on, where the data banks contain locational references such as a district, or the actual boundaries of land parcels. GISs are run on the all spectrum of computer systems ranging from personal computers (PCs) to multi user supercomputers, and are available in a wide variety of software languages. There are number of tools that are essential for effective GIS establishment

which

are

computer,

digitizer,

GPS

(Global

Positioning System), plotter, and network. CD-ROM drive, printer and of course software which links all of the equipment to run properly. Canada has been a pioneer in the development of GIS . The Canada Geographic Information System (CGIS). Initiated in 1963 by the Agriculture Rehabilitation and Development Agency, was the first operational land resources GIS. Rajdhani Unnoyan Kartipakkha (RAJUK) installed GIS in 1993.In this organization the main field of GIS application is urban planning. Here, the GIS activity mainly concentrates on mapping and data management for development planning of Dhaka Metropolitan Area. RAJUK also prepared urban landuse planning 11

map and infrastructure map at strategic 1:50000 to detailed 1:3960 using spatial and attribute data. In 1995 Roads and Highways Department (RHD) under an Institutional Development Components (IDC) Project sponsored by Overseas Development Agency (ODA) completed GIS mapping programmes to create national transport network. In 1996 the project also successfully built a comprehensive e geographical database for the road and rail sectors, which started operation in 1997. Survey of Bangladesh (SOB) mainly installed GIS technology for making and publishing digital maps. For this reason SOB works in cooperation with other national organizations like SPARRSO, BBS, DLRS and international organizations like JICA (Japan International cooperation Agency), IGN of France. ITC of Netherlands and Ordinance Survey of England.The major GIS installed in 1991) activities of SPARRSO are to facilitate remote sensing and other spatial and attribute data for various applications in environment and resource sectors. The successful projects of SPARRSO in this regard

are

Crop,

Forest

cover

mapping,

Shrimp

Culture

Potentiality Mapping, Census Mapping, Monitoring of Ecological Changes, and landuse Mapping. Soil Resources Development Institute (SRDI) render supports for preparing Thana Land and Soil Utilization Guides including a soil database, soil fertility and landuse monitoring. Salinity monitoring and preparation of soil and landuse related maps. All these activities of mapping and monitoring systems are GIS related.

12

Surface Water modeling Center (SWMC) is using GIS as a data processing, modeling and planning tool. By using GIS, SWMC is succeeded in monitoring optimum operation of Karnafuli Hydro Power Station, arsenic contamination of groundwater and crop damage assessment. They are also successful in GIS based software development. Interactive Information System (IIS) is one of the key development software, which combines topographic maps prepared under Geographical Information System and field information

of

channels,

structures,

roads,

embankments,

homesteads stored in a Rational Database Management System (RDMS). The Water Resources Planning Organization (WARPO) prepared and updated National Water Resources Database (NWRD) for preparing the national Water Policy adopted by the Government of Bangladesh. The database is designed with SQL (Structural Query Language) in back-end and GIS based graphical user interfaces in front-end. The primary activity of NWRD is to meet the demand of water resource planners for a consolidated and reliable data bank. All the universities of Bangladesh installed GIS for their academic curriculum in order to create skilled manpower for the country. The department of Geography and Environment, Jahangirnagar University set up GIS lab in 1992. The following year several other university departments established GIS lab. These are the department of Geography and Environment, University of Dhaka; the

department of

Geography and Environmental

Studies,

Rajshahi University; Urban and Rural Planning Discipline. Khulna University; the Department of Urban and Regional Planning (URP)

13

and Bangladesh University of Engineering and Technology (BUET). Recently the department of Geology and the department of Soil. Water and Environment, both form Dhaka University and the

department

of

Geography,

Chittagong

University

also

established GIS lag for research purposes. Some other GIS installed organizations and companies are Bangladesh

Inland

Water

Transport

Authority

(BIWTA).

Bangladesh Water Board (BWBD), CIPROCO Computers Ltd. Cooperation of American Relief in Everywhere (Care), Directorate of Land Records and Surveys (DLRS). Danish International Development Agency (DANIDA). Development Design Consultants (DDC).

Department

of

Environment

(DOE).

GEOSRV

Ltd.

Geographical Solutions Research Center (GSRC) Ltd. International Center for Diarrhoea Disease Research. Bangladesh (ICDDR.B). Japan International Cooperation Agency (JICA), Natural Resources Programs (NRP), Bangladesh Project of the Asiatic Society of Bangladesh, The Mappa etc.

1.6 Application of GIS: The applications or uses for a GIS are endless, wherever spatial features need to be modeled and analyzed. Some common examples are listed below. Environmental Resource Management Environmental applications lend themselves very well to GIS because they often require the integration of numerous different data sets during the analysis, since environmental systems tend to be complex and composed of inter-related sub-systems.

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Particular applications include river channel maintenance, coastal defiance, forestry and national park management. Emergency Planning and Routing The provision of optimum locations for emergency service centre can also be aided by GIS analysis of the various parameters such as access to roads, population density and various health indicators. Network analysis can be utilized to define optimum routes, such as shortest or fastest, for the routing of emergency service vehicles. Provision of Health, Educational Or Retail Services Consideration of the spatial distribution of different sectors of the population, their health and socio-economic characteristics and the accessibility to transport routes plus the location of existing facilities are required prior to the effective location of new facilities or the allocation of new services.

Fig.2.Aplicatoin of GIS

15

Facility Management for the Utilities The utility industries tend to have vast numbers of facilities to manage in order to provide large customer regions with an efficient and reliable service. Gas, water, electricity and sewage utilities for instance own a lot of land, buildings, cables, pipes and other physical facilities which need monitoring, maintaining and managing in order to provide an effective service. Highway Maintenance and Accident Monitoring Roads and motorways need to be maintained and monitored for accident trouble spots. GIS are ideal for representing the spatial relationships between sections and storing the associated information tied to each section of road. Maintenance records can also be incorporated into the GIS and so provide up to date displays of the state of the road network and the sections which require immediate maintenance. Market Analysis The spatial distribution of the population and particularly the different age groups and socio-economic sectors are essential information to the market analyst attempting to discover the most suitable place to launch a new product or sell a particular brand. The effectiveness of any given marketing strategy can also be modeled and evaluated. Population Analysis and Prediction The spatial distribution of the population and the predicted level of a population are essential information to planners and developers when deciding what type of facilities need to be constructed now in order to best suit the needs of the future population. Census data thus provide an important input to GIS. GIS essentially enable the relationships between various spatial features to be visualized and analyzed which in turn encourages a better understanding of the interactions between the various features. GIS also enable the data to be manipulated and analyzed quickly and flexibly in a single system which is an extremely powerful capability.

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MAJOR AREAS OF PRACTICAL APPLICATION Street network-based ➠

address matching - finding locations given street addresses

➠

vehicle routing and scheduling

➠

location analysis, site selection

➠

development of evacuation plans

Natural resource-based ➠

management of wild and scenic rivers, recreation resources, floodplains, wetlands, agricultural lands, aquifers, forests, wildlife

➠

Environmental impact analysis (EIA)

➠

view shed analysis

➠

hazardous or toxic facility sitting

➠

groundwater modeling and contamination tracking

➠

wildlife habitat analysis, migration routes planning

Land parcel-based ➠

zoning, subdivision plan review

➠

land acquisition

➠

environmental impact statements

➠

water quality management

➠

maintenance of ownership

Facilities management ➠

locating underground pipes, cables

➠

balancing loads in electrical networks

➠

planning facility maintenance

➠

tracking energy use

1.7 Advantages of GIS:

17

In theory, all GIS processes can be undertaken manually. Before GIS, analysis procedures would have been manually undertaken using transparent overlays or run through very slow and cumbersome machines with far less power than the machines of today. The essential advantage of modern GIS, however, is that all the functionality for working with multiple sets of geographic information are grouped and automated within one piece of software. In addition it benefits from modern computer efficiency and speed. Overall, the use of modern GIS offers many advantages over paper maps: • • • • • • •

Can cope with larger amounts of data Can cover large study areas (the whole world if necessary) Can conveniently select any sub-study area Can cope with unlimited and frequent edits and changes More robust and resistant to damage Faster and more efficient Requires less person time and mo

1.8 Limitation of GIS: ➠

It is not easy to understand

➠

GIS data is not available

➠

GIS data is more expensive

➠

it is more complex for unauthorized person

➠

it is more highly-thematic concept

➠

it is not easily erasable

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CHAPTER TWO

2.1 Components of a GIS

Fig.3 Components of GIS

•

Hardware: The computer on which a GIS operates. A wide range of hardware types, from centralized computer servers 19

to desktop computers used in stand-alone or networked configurations.

Fig.4.Components of Hardware •

•

•

Software: GIS software provides the functions and tools needed to store, analyze, and display geographic information. Key software components are o tools for the input and manipulation of geographic information o a database management system (DBMS) o tools that support geographic query, analysis, and visualization. o a graphical user interface(GUI) for easy access to tools. o Major GIS softwares: Arc/Info by ESRI, Intergraph by Intergraph, MapInfo by MapInfo, etc. Data: Possibly the most important component of a GIS is the data. Geographic data and related tabular data can be collected in house or purchased from a commercial data provider. A GIS will integrate spatial data with other data resources and can even use a DBMS, used by most organizations to organize and maintain their data, to manage spatial data. People: GIS technology is of limited value without the people who manage the system and develop plans for 20

•

applying it to real world problems. GIS users range from technical specialists who design and maintain the system to those who use it to help them perform their everyday work. Methods: A successful GIS operates according to a welldesigned plan and business rules, which are the models and operating practice unique to each organization.

GIS Functional/Procedural Elements •

Data acquisition: The process of identifying and gathering the data required for your application. o Gathering new data by preparing large-scale maps of field observations, or by contracting for aerial photography. o Locating and acquiring existing data, such as maps, aerial and ground photography, surveys of many kinds, and documents, from archives and repositories. Preprocessing: Manipulating the data in several ways so that it may be entered it into the GIS. o

o

Data format conversion: extracting information from maps, photographs, and printed records and then recording this information in a computer database. Identifying the locations of objects in the original data.

Data management: The creation of and access to the database itself. •

Manipulation and analysis: focus of attention for a user of the system. The analytic operators that work with the database contents to derive new information.

21

. Product generation: Final outputs from the GIS like statistical reports, maps, and graphics of various kinds. •

2.2Process of GIS Procedures include how the data will be retrieved, input into the system, stored, managed, transformed, analyzed, and finally presented in a final output. Modern GIS technologies use digital information, for which various digitized data creation methods are used. The most common method of data creation is digitization, where a hard

22

copy map or survey plan is transferred into a digital medium through the use of a computer-aided design (CAD) program, and geo-referencing capabilities. With the wide availability of orthorectified imagery (both from satellite and aerial sources), headsup digitizing is becoming the main avenue through which geographic data is extracted. Heads-up digitizing involves the tracing of geographic data directly on top of the aerial imagery instead of by the traditional method of tracing the geographic form on a separate digitizing tablet (heads-down digitizing). Relating information from different sources GIS uses spatio-temporal (space-time) location as the key index variable for all other information. Just as a relational database containing text or numbers can relate many different tables using common key index variables, GIS can relate otherwise unrelated information by using location as the key index variable. The key is the location and/or extent in space-time. Any variable that can be located spatially, and increasingly also temporally, can be referenced using a GIS. Locations or extents in Earth space–time may be recorded as dates/times of occurrence, and x, y, and z coordinates representing, longitude, latitude, and elevation, respectively. These GIS coordinates may represent other quantified systems of temporo-spatial reference (for example, film frame number, stream gage station, highway milemarker, surveyor benchmark, building address, street intersection, entrance gate, water depth sounding, POS or CAD drawing origin/units). Units applied to recorded temporal-spatial data can vary widely (even when using exactly the same data, see map projections), but all Earth-based spatial–temporal location and extent references should, ideally, be relatable to one another and ultimately to a "real" physical location or extent in space–time. GIS uncertainties GIS accuracy depends upon source data, and how it is encoded to be data referenced. Land surveyors have been able to provide a high level of positional accuracy utilizing the GPS derived positions.[15] the high-resolution digital terrain and aerial imagery, [16] the powerful computers, Web technology, are changing the quality, utility, and expectations of GIS to serve society on a 23

grand scale, but nevertheless there are other source data that has an impact on the overall GIS accuracy like: paper maps that are not found to be very suitable to achieve the desired accuracy since the aging of maps affects their dimensional stability. Data representation GIS data represents real objects (such as roads, land use, elevation, trees, waterways, etc.) with digital data determining the mix. Real objects can be divided into two abstractions: discrete objects (e.g., a house) and continuous fields (such as rainfall amount, or elevations). Traditionally, there are two broad methods used to store data in a GIS for both kinds of abstractions mapping references: raster images and vector. Points, lines, and polygons are the stuff of mapped location attribute references. A new hybrid method of storing data is that of identifying point clouds, which combine three-dimensional points with RGB information at each point, returning a "3D color image". GIS Thematic maps then are becoming more and more realistically visually descriptive of what they set out to show or determine Data capture Data capture—entering information into the system—consumes much of the time of GIS practitioners. There are a variety of methods used to enter data into a GIS where it is stored in a digital format.

Fig.5 Example of hardware for mapping (GPS and laser rangefinder) and data collection (rugged computer). The current trend for GIS is that accurate mapping and data analysis are completed while in the field. 24

Existing data printed on paper or PET film maps can be digitized or scanned to produce digital data. A digitizer produces vector data as an operator traces points, lines, and polygon boundaries from a map. Scanning a map results in raster data that could be further processed to produce vector data. The majority of digital data currently comes from photo interpretation of aerial photographs. Soft-copy workstations are used to digitize features directly from stereo pairs of digital photographs. These systems allow data to be captured in two and three dimensions, with elevations measured directly from a stereo pair using principles of photogrammetry. Analog aerial photos must be scanned before being entered into a soft-copy system, for high quality digital cameras step is skipped. Satellite remote sensing provides another important source of spatial data. Here satellites use different sensor packages to passively measure the reflectance from parts of the electromagnetic spectrum or radio waves that were sent out from an active sensor such as radar. Remote sensing collects raster data that can be further processed using different bands to identify objects and classes of interest, such as land cover. When data is captured, the user should consider if the data should be captured with either a relative accuracy or absolute accuracy, since this could not only influence how information will be interpreted but also the cost of data capture. Raster-to-vector translation Data restructuring can be performed by a GIS to convert data into different formats. For example, a GIS may be used to convert a satellite image map to a vector structure by generating lines around all cells with the same classification, while determining the cell spatial relationships, such as adjacency or inclusion. More advanced data processing can occur with image processing, a technique developed in the late 1960s by NASA and the private sector to provide contrast enhancement, false color rendering and a variety of other techniques including use of two dimensional Fourier transforms.

25

Projections, coordinate systems and registration The earth can be represented by various models, each of which may provide a different set of coordinates (e.g., latitude, longitude, elevation) for any given point on the Earth's surface. The simplest model is to assume the earth is a perfect sphere. As more measurements of the earth have accumulated, the models of the earth have become more sophisticated and more accurate Spatial analysis with GIS GIS spatial analysis is a rapidly changing field, and GIS packages are increasingly including analytical tools as standard built-in facilities, as optional toolsets, as add-ins or 'analysts'. In many instances these are provided by the original software suppliers (commercial vendors or collaborative non commercial development teams), whilst in other cases facilities have been developed and are provided by third parties. Slope and aspect Slope, aspect and surface curvature in terrain analysis are all derived from neighborhood operations using elevation values of a cell's adjacent neighbors. Authors such as Skidmore,[21] Jones[22] and Zhou and Liu[23] have compared techniques for calculating slope and aspect. Slope is a function of resolution, and the spatial resolution used to calculate slope and aspect should always be specified.

Zhou and Liu[23] describe another algorithm for calculating aspect, as follows:

26

Data analysis It is difficult to relate wetlands maps to rainfall amounts recorded at different points such as airports, television stations, and high schools. A GIS, however, can be used to depict two- and threedimensional characteristics of the Earth's surface, subsurface, and atmosphere from information points. For example, a GIS can quickly generate a map with isopleth or contour lines that indicate differing amounts of rainfall. Such a map can be thought of as a rainfall contour map. Many sophisticated methods can estimate the characteristics of surfaces from a limited number of point measurements. A twodimensional contour map created from the surface modeling of rainfall point measurements may be overlaid and analyzed with any other map in a GIS covering the same area. Topological modeling A GIS can recognize and analyze the spatial relationships that exist within digitally stored spatial data. These topological relationships allow complex spatial modeling and analysis to be performed. Topological relationships between geometric entities traditionally include adjacency (what adjoins what), containment (what encloses what), and proximity (how close something is to something else). Geometric Networks Geometric networks are linear networks of objects that can be used to represent interconnected features, and to perform special spatial analysis on them. A geometric network is composed of edges, which are connected at junction points, similar to graphs in mathematics and computer science. Just like graphs, networks can have weight and flow assigned to its edges, which can be used to represent various interconnected features more accurately. Hydrological modeling GIS hydrological models can provide a spatial element that other hydrological models lack, with the analysis of variables such as slope, aspect and watershed or catchment area. Terrain analysis 27

is fundamental to hydrology, since water always flows down a slope. As basic terrain analysis of a digital elevation model (DEM) involves calculation of slope and aspect, DEMs are very useful for hydrological analysis. Slope and aspect can then be used to determine direction of surface runoff, and hence flow accumulation for the formation of streams, rivers and lakes. Cartographic modeling The term "cartographic modeling" was probably coined by Dana Tomlin in his PhD dissertation and later in his book which has the term in the title. Cartographic modeling refers to a process where several thematic layers of the same area are produced, processed, and analyzed. Tomlin used raster layers, but the overlay method (see below) can be used more generally. Operations on map layers can be combined into algorithms, and eventually into simulation or optimization models. Map overlay The combination of several spatial datasets (points, lines or polygons) creates a new output vector dataset, visually similar to stacking several maps of the same region. These overlays are similar to mathematical Venn diagram overlays. A union overlay combines the geographic features and attribute tables of both inputs into a single new output. An intersect overlay defines the area where both inputs overlap and retains a set of attribute fields for each. A symmetric difference overlay defines an output area that includes the total area of both inputs except for the overlapping area. Geostatistics Geostatistics is a point-pattern analysis that produces field predictions from data points. It is a way of looking at the statistical properties of those special data. It is different from general applications of statistics because it employs the use of graph theory and matrix algebra to reduce the number of parameters in the data. Only the second-order properties of the GIS data are analyzed. When phenomena are measured, the observation methods dictate the accuracy of any subsequent analysis. Due to the nature of the data (e.g. traffic patterns in an urban environment; weather patterns over the Pacific Ocean), a 28

constant or dynamic degree of precision is always lost in the measurement. This loss of precision is determined from the scale and distribution of the data collection. Digital elevation models (DEM), triangulated irregular networks (TIN), edge finding algorithms, Thiessen polygons, Fourier analysis, (weighted) moving averages, inverse distance weighting, kriging, spline, and trend surface analysis are all mathematical methods to produce interpolative data. Address geocoding Geocoding is interpolating spatial locations (X,Y coordinates) from street addresses or any other spatially referenced data such as ZIP Codes, parcel lots and address locations. A reference theme is required to geocode individual addresses, such as a road centerline file with address ranges. The individual address locations have historically been interpolated, or estimated, by examining address ranges along a road segment. These are usually provided in the form of a table or database. Reverse geocoding Reverse geocoding is the process of returning an estimated street address number as it relates to a given coordinate. For example, a user can click on a road centerline theme (thus providing a coordinate) and have information returned that reflects the estimated house number. This house number is interpolated from a range assigned to that road segment. If the user clicks at the midpoint of a segment that starts with address 1 and ends with 100, the returned value will be somewhere near 50. Note that reverse geocoding does not return actual addresses, only estimates of what should be there based on the predetermined range. Data output and cartography Cartography is the design and production of maps, or visual representations of spatial data. The vast majority of modern cartography is done with the help of computers, usually using a GIS but production quality cartography is also achieved by importing layers into a design program to refine it. Most GIS

29

software gives the user substantial control over the appearance of the data. Cartographic work serves two major functions: First, it produces graphics on the screen or on paper that convey the results of analysis to the people who make decisions about resources. Wall maps and other graphics can be generated, allowing the viewer to visualize and thereby understand the results of analyses or simulations of potential events. Second, other database information can be generated for further analysis or use. An example would be a list of all addresses within one mile (1.6 km) of a toxic spill. Graphic display techniques Traditional maps are abstractions of the real world, a sampling of important elements portrayed on a sheet of paper with symbols to represent physical objects. People who use maps must interpret these symbols. Topographic maps show the shape of land surface with contour lines or with shaded relief. Today, graphic display techniques such as shading based on altitude in a GIS can make relationships among map elements visible, heightening one's ability to extract and analyze information. For example, two types of data were combined in a GIS to produce a perspective view of a portion of San Mateo County, California. •

•

The digital elevation model, consisting of surface elevations recorded on a 30-meter horizontal grid, shows high elevations as white and low elevation as black. The accompanying Landsat Thematic Mapper image shows a false-color infrared image looking down at the same area in 30-meter pixels, or picture elements, for the same coordinate points, pixel by pixel, as the elevation information.

Spatial ETL Spatial ETL tools provide the data processing functionality of traditional Extract, Transform, Load (ETL) software, but with a primary focus on the ability to manage spatial data. They provide GIS users with the ability to translate data between different 30

standards and proprietary formats, transforming the data en-route.

whilst

geometrically

GIS Data Mining GIS or spatial data mining is the application of data mining methods to spatial data. Data mining, which is the partially automated search for hidden patterns in large databases, offers great potential benefits for applied GIS-based decision-making. Typical applications including environmental monitoring. A characteristic of such applications is that spatial correlation between data measurements require the use of specialized algorithms for more efficient data analysis.

CHAPTER THREE 3.1 GIS DATA AND DATA CLASSIFICATION A GIS stores information about the world as a collection of thematic layers that can be linked together by geography. This simple but extremely powerful and versatile concept has proven invaluable for solving many real-world problems from tracking delivery vehicles, to recording details of planning applications, to modeling global atmospheric circulation. The thematic layer approach allows us to organize the complexity of the real world into a simple representation to help facilitate our understanding of natural relationships.

31

Fig.6 GIS DATA It is necessary to know the GIS data, if any one work in GIS software by computer. If the data is wrong the result will be wrong or it is impossible to represent the accurate information on the map. Any collection of related facts arranged in a particular format; often, the basic elements of information that are produced, stored or processed by a computer. All GIS software has been designed to handle spatial data. Spatial data are characterized by information about position, connections with other features and details of non-spatial characteristics (Burrough, 1986), Spatial data is as a series of thematic layers. Spatial data, represented as either layers or objects, must be implied before they can be stored in the computer. A common way of doing this is to break down all geographic features into three basic entries is a component. These are ➠

Points.

➠

Line. 32

➠

Polygon or Area.

Fig 7. Components of Geographic Features ➠

Points: Points are used to represent features that are too small to be represented as areas. An example is a postbox.

➠

Lines: Lines are used to represent features that are linear in nature, for example roads or rivers. They can be used to represent linear features that do not exist in reality, such as administrative boundaries or international borders.

➠

Polygon or Areas: Areas are represented by a closed set of lines and are used to define features such as fields, buildings or administrative areas. Area entities are often referred to as polygons. As with line features, some of these polygons exists on the ground, while others are imaginary.

Two types of polygon can be identified: (a) Island polygon. (b) Adjacent polygon.

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3.1.1 Two types of GIS data :

GIS Data

Non-Spatial Data (AttribuTe Data)

Spatial Data

Raster Data

Vector Data

Fig. 8 : Types of GIS Data a. Spatial Data: Place base view of any place is called spatial

data e.g. River, Canal, house, hill – mountain, cultivate land, vegetation etc.

of any places. Generally spatial data of

earth surface remain viewed in a certain place. In following shows a figure on the basis of spatial data. The following diagram reflects the two primary spatial data encoding techniques. These are vector and raster. Image data utilizes techniques very similar to raster data, however typically lacks the internal formats required for analysis and modeling of the data. Images reflect pictures or photographs of the landscape.

Traditionally spatial data has been stored and presented in the form of a map. Two basic types of spatial data models have evolved for storing geographic data digitally. These are referred to as: i.

Raster Data

ii.

Vector Data •

Raster data: A spatial data model that defines space as an array of equally sized cells arranged in 34

rows and columns. Each cell contains an attribute value

and

location

coordinates.

Unlike

vector

structure, which stores coordinates explicitly, raster coordinates are contained in the ordering of the matrix. Groups of cells that share the same value represent geographic features.

Fig. 9 : Raster Data •

Vector data: A coordinate-based data model that represents geographic features as points, lines and polygons. Each point feature is represented as a single coordinate pair, while line and polygon features are represented as ordered lists of vertices. Attributes are associated with each feature, as opposed to a raster data model, which associates attributes with grid cells.

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Fig. 10: Vector Data

b. Non-Spatial Data: Non-Visible qualitative data is called

the non-spatial data. These data may be changed. E.g. education rate of any area, per capita income, maternal mortality rate, population density etc. Non-spatial data is also called the attribute data. GIS technology makes a map informative by the uses of non-spatial data. 3.2 .1 Source of GIS Data: The following data sources are widely used: 1. Analog Map • Elevation • Soil • Land Use • Climate 2. Aerial Photographs • Land use (urban) • DEM 3. Satellite image 36

•

Land use (Regional) • Vegetation • Temperature • DEM 4. Ground survey with GPS • Detailed information 5. Reports and Publications • Attributes • Statistics

Data source for GIS

Analog maps

Aerial photographs

Satellite image

Elevation

DEM

Land use (regional)

Land use

Land use (Urban)

Vegetation

Climate

Temperature DEM

Ground survey with GPS

Reports and publications

Detailed

Attributes

Information

Statistics

On land use

Agriculture

Land type

Industry

Fig. 11: Shows the source of GIS Data

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3.2.2 Data Acquisition Method : Data acquisition in GIS refers to all aspects of eructing spatial data from all available sources and converting then to a standard digital form. This requires tools such as interactive computer screen and mouse, digitizing word processor and spreadsheet programs, scanners and device necessary for reading data already written on magnetic media such as types or CD Roms. (A) Terrain Data from satellite Remote sensing: The terrain data acquired through sensors on board satellite platforms being in digital format can be directly used after preprocessing for preparing a GIS database. These data are coded in picture element called pixel and stored in the form of two dimensional matrix that contains a number represented the amount of reflected electromagnetic radiation received in a given band.. (B) Terrain data from existing maps: The acquisition of digital data by digitizing existing maps is comparatively cheaper, and requires less time compared to other methods. The topographical maps covering large part of a country are mostly available, and the required information for a particular job acquired from these maps by digitization. The digitizing of paper maps is done using a spatial data capturing device caused a digitizer. In recent years, the importance of the digitier has diminished as a result of growing use of scanners and the increasing availability of digital data from a govt. and commercial data suppliers. (C) Terrain Data connection by photography: When the area of interest is too expensive or too rugged, the photogram metric method is employed to collect digital terrain data using appropriate photogram metric instrument such as analog stereo plotter, analytical plotter or using photogrammetry uses digital images instead of photographic diapositive. The digital image may be obtained either resolution or by the remote sensing imaging system. A digital photogram metric work station which produce digital image, including hardware, software, peripherals such as digital camera, film scanner, plotter etc. 38

(D) Terrain data from field surveying method: Terrain data in digital form can be obtained directly by field surveying methods by employing instrument such as total station and GPS. Total station is capable of electronically , measuring both angles and distance and per forming computation to obtain horizontal distance slope distance, difference in elevation, and elevation of points (E) Digital Terrain Data from internet: The internet is a vast network of digital computers. The www is a tern used synonymously with the internet. It is in fact the main information tool of the internet through which the data written and “web pages” are accessed. These are available t the user world wide through a “web server” and viewed by users at remote locations using “web browser” software. For GIS users, the www provides data and source of information (F) Digital terrain data by GPS: GPS is a satellite based surveying system to obtain highly accurate digital terrain data electronically in the form of X,Y,Z, co-ordinates. There are two basic field methods of GPS measurement static and different types of Data acquisition method Data source method Equipments Cost Analog map Marceal Digitizer Cheap digitizing Semi Scanner High automatic scanning Aerial Analytical 3rd (Analog High photograph photography stecopotter) Digital Digital photo Very High photogrametr work station y Satellite Visual image man or image cheap Image mterpretation zoom scope Digital image Image High processing processing system Ground Field GPS Very High survey measurement Total Station Very High 39

Previous report

key entry

board PC. key board

Cheap

3.3 GIS Data Model: Tsichritzis and Lochovsky (1977) define a data model as a set of guidelines for the representation of the logical organization of the data in a database consisting of named logical units of data and the relationships between them. While the concept of the data model is used in a variety of ways by numerous disciplines, a digital geographic data model is generally defined as an information structure which allows the user to store specific phenomena as distinct representations, and enables the user to manipulate the phenomena when held in the system as data The data model represents a set of guidelines to convert the real world (called entity) to the digitally and logically represented spatial objects consisting of the attributes and geometry. The attributes are managed by thematic or semantic structure while the geometry is represented by geometric-topological structure (Shunji 1999). 3.3.1DATA MODELS USED IN GIS A great number and variety of data models has been used in GIS. They are listed below (John, 1997). 1. General Models 1.1 Spaghetti model Basic data models 40

 Vector  Raster (more generally, tessellation model) Spatial models  Plane geometry models  Plane topology models Surface models  Digital Elevation Models (DEMs)  Triangular Irregular Network (TIN) model Mathematical models Conceptual models  Entity-Relationship (ER) model  Enhanced Entity-Relationship (EER) model An implementation model Relational model Semantic (?) models  Object-oriented model  Functional model Hierarchical models Quadtrees, strip trees

2. Standards Spatial Data Transfer Specification (SDTS) 3. Proprietary models 3.3.2Types Of GIS Data Model: The data model represents a set of guide lines to convert the real world to the digitally and logically represented spatial objects consisting of the attribute and geometry. There are two types of data model. • Raster data model

41

• Vector data model 3.3.2.1: Raster data model: A spatial data model that defines space as an array of equally sized cells arranged in rows and columns. Each cell contains an attribute values and location co ordinates. Raster data are stored in the computer as a matrix. The cell is referenced by lines and elements. Each line is a computer record, each record will contain the values fall all elements in the lines. A raster data model is variously called a grid, a raster map, a surface cover. Source of raster data model: • Much data comes in this form • Image from remote sensing • Scanned maps • Elevation data from USGS Advantages of Raster Data:  It is simple data structure  It is good at representing continuous data  Representing multiple feature types  Technology is inexpensive, dynamic, development is easy.  Area and polygon analysis s simple  Remote sensing on satellite store data in raster format Disadvantage of Raster data:  It is large data volume  There can be a serious of detail with large pixel sizes  Linear types of analysis is more difficult  Topographical relationship are more difficult to represent

42

 Advanced technology is difficult to establish

Application:  Topographic and thematic mapping  Terrain modeling  Hydrologic analysis.  Wild life habit analysis  crop production estimates 3.3.2.2: Vector data model: A coordinate based data model that represent geographic feature as point, line, polygons. Each point feature is represented as a single coordinate pair, while line and polygon feature is represented as ordered list of vertices. Attributes are associated feature, as opposed to a raster da model, which associate attribute with grid cells. Source of data:  DIME and TIGER Files from US cencus  Census data tabular Advantages:  Data can be represented in its original resolution and form without generalization.  Very small feature can be shown and all features can be accurately drawn.  Linear type of analysis are easily performed.  Ac curate geographic location of data is maintained Disadvantage: 43

 It is more complex data structure  Data capture can be very slow  Area or polygon analysis are difficult  Overlay operation are more difficult to implement  Continuous data, such as elevation data is not effectively represented in vector form  Software, hardware vector system often expensive

3.4 Database management systems: A set of computer programs that organize the information in a database according to a conceptual scheme and provide tools for data input, verification, storage, modification and retrieval. Database Systems Objectives To

understand

the

fundamental

concepts

technology underlying database systems: Modern database systems: Object-relational databases Multimedia support for databases Database design methodology Database management systems

Functionalities of DBMSs Specifying the database structure 44

and

advanced

Data definition language Manipulation of the database Query processing and query optimization Integrity enforcement Integrity constraints Concurrent control Multiple user environment Crash recovery Security and authorization Database Approach

Fig12 .:Database Approach Role in an Information System

Fig.13: Role in an Information System 3.5 Georeferencing 45

To georeference something means to define its existence in physical space. That is, establishing its location in terms of map projections or coordinate systems. The term is used both when establishing the relation between raster or vector images and coordinates, and when determining the spatial location of other geographical features. Examples would include establishing the correct position of an aerial photograph within a map or finding the geographical coordinates of a place name or street address. This procedure is thus imperative to data modeling in the field of geographic information systems (GIS) and other cartographic methods. When data from different sources need to be combined and then used in a GIS application, it becomes essential to have a common referencing system. This is brought about by using various georeferencing techniques. Most georeferencing tasks are undertaken either because the user wants to produce a new map or because they want to link two or more different datasets together by virtue of the fact that they relate to the same geographic locations. Need •

•

•

•

•

Georeferencing is crucial to making aerial and satellite imagery, usually raster images, useful for mapping as it explains how other data, such as the above GPS points, relate to the imagery. Very essential information may be contained in data or images that were produced at a different point of time. It may be desired either to combine or compare this data with that currently available. The latter can be used to analyze the changes in the features under study over a period of time. Different maps may use different projection systems. Georeferencing tools contain methods to combine and overlay these maps with minimum distortion. Using georeferencing methods, data obtained from surveying tools like total stations may be given a point of reference from topographic maps already available. It may be required to establish the relationship between social survey results which have been coded with postal codes or street addresses and other geographic areas such as census zones or other areas used in public administration or service planning.

46

Methods There are various GIS tools available that can transform image data to some geographic control framework, like ArcMap, PCI Geomatica, or ERDAS Imagine. One can georeference a set of points, lines, polygons, images, or 3D structures. For instance, a GPS device will record latitude and longitude coordinates for a given point of interest, effectively georeferencing this point. A georeference must be a unique identifier. In other words, there must be only one location for which a georeference acts as the reference. Images may be encoded using special GIS file formats or be accompanied by a world file. To georeference an image, one first needs to establish control points, input the known geographic coordinates of these control points, choose the coordinate system and other projection parameters and then minimize residuals. Residuals are the difference between the actual coordinates of the control points and the coordinates predicted by the geographic model created using the control points. They provide a method of determining the level of accuracy of the georeferencing process. In situations where data has been collected and assigned to postal or area codes, it is usually necessary to convert these to geographic coordinates by use of a definitive directory or gazetteer file. Such gazetteers are often produced by census agencies, national mapping organizations or postal service providers. At their simplest, these may simply comprise a list of area codes or place names and another list of corresponding codes, names or coordinate locations. The range and purpose of the codes available is country-specific. An example is the UK's National Statistics Postcode Directory which shows each postcode's membership of census, administrative, electoral and other geographical areas. In this case, the directory also provides dates of creation and deletion, address counts and an Ordnance Survey grid reference for each postcode, allowing it to be mapped directly. Such gazetteer files support many web-based mapping systems which will place a symbol on a map or undertaken analysis such as route-finding, on the basis of postal codes, addresses or place names input by the

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3.6 Digitizing The process of representing an analogue signal or an image by a discrete set of its points is known as Digitizing. This data after conversion is in the binary format, which is directly readable by computer. The data to be converted can be a text, an image, audio or a video. The analogue signals are variable whereas the digital format is the discrete one. These discrete units are called as bits. These bits (8) organized in groups are known as byte. The digital signals are mainly represented in the form of sequence of integers. These integers can be converted back to analogue signal that are approximately similar to the original analogue signals. Digitizing is done by reading an analogue signal ‘A’, and at regular time intervals, representing the value of ‘A’ at that point by an integer. Types of Digitizing: •

•

•

Manual Digitizing: It is done using digitizing tablet. The operator manually traces all the lines from his hardcopy map and creates identical digital map on the computer. It is very time consuming and level of accuracy is also not very good. Heads-up Digitizing: It is similar to manual digitizing in the way that lines have to be drawn manually but directly on the computer screen. So in this level of accuracy increases and time taken decreases. Interactive tracing method: It is improvement over Heads-up digitizing in terms of speed and accuracy.

Automatic Digitizing: It is automated raster to vector conversion using image processing and pattern recognition techniques. In this technique computer traces all the lines, which results in high speed and accuracy along with improved quality of images. Device used for digitization is known as digitizer. It is an electromagnetic device consisting of a table upon which a map or a document to be scanned is placed. This device enters the spatial coordinates of mapped features from a map or a •

48

document to the computer. It is done with the help of a mouse or a hand held magnetic pen. The most commonly used digitizers are: • •

Electrical orthogonal fire wire grid digitizer. Electrical wave phase type digitizer.

3.7 Digital elevation model A digital elevation model is a digital model or 3D representation of a terrain's surface — commonly for a planet (including Earth), moon, or asteroid — created from terrain elevation data.

Mars

Fig.14 3D rendering of a DEM of Tithonium Chasma on

Types of DEM A DEM can be represented as a raster (a grid of squares, also known as a heightmap when representing elevation) or as a vector-based triangular irregular network (TIN). The TIN DEM dataset is also referred to as a primary (measured) DEM, whereas 49

the Raster DEM is referred to as a secondary (computed) DEM. DEMs are commonly built using remote sensing techniques, but they may also be built from land surveying. DEMs are used often in geographic information systems, and are the most common basis for digitally-produced relief maps. The DEM could be acquired through techniques such as photogrammetry, LiDAR, IfSAR, land surveying, etc. (Li et al. 2005). While a DSM may be useful for landscape modeling, city modeling and visualization applications, a DTM is often required for flood or drainage modeling, land-use studies, geological applications, and much more.

Production The quality of a DEM is a measure of how accurate elevation is at each pixel (absolute accuracy) and how accurately is the morphology presented (relative accuracy). Several factors play an important role for quality of DEM-derived products: • • • • • • •

terrain roughness; sampling density (elevation data collection method); grid resolution or pixel size; interpolation algorithm; vertical resolution; terrain analysis algorithm; Reference3D products include quality masks that give information on: the coastline, lake, snow, clouds, correlation etc....

Methods for obtaining elevation data used to create DEMs • • • • • •

LIDAR Stereo photogrammetry from aerial surveys Block adjustment from optical satellite imagery Interferometry from radar data Real Time Kinematic GPS Topographic maps 50

• • • •

Theodolite or total station Doppler radar Focus variation Inertial surveys

Uses Common uses of DEMs include: • • • • • • • • • • • • • • • • • • • •

Extracting terrain parameters Modeling water flow or mass movement (for example avalanches and landslides) Creation of relief maps Rendering of 3D visualizations. 3D flight planning Creation of physical models (including raised-relief maps) Rectification of aerial photography or satellite imagery. Reduction (terrain correction) of gravity measurements (gravimetry, physical geodesy). Terrain analyses in geomorphology and physical geography Geographic Information Systems (GIS) Engineering and infrastructure design Global positioning systems (GPS) Line-of-sight analysis Base mapping Flight simulation Precision farming and forestry Surface analysis Intelligent transportation systems (ITS) Auto safety / Advanced Driver Assistance Systems (ADAS) Archaeology

Sources A free DEM of the whole world called GTOPO30 (30 arcsecond resolution, approx. 1 km) is available, but its quality is variable and in some areas it is very poor. A much higher quality DEM from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument of the Terra satellite is also freely available for 99% of the globe, and represents elevation at a 30 meter resolution. A similarly high resolution was previously only available for the United States territory under the Shuttle Radar Topography Mission (SRTM) data, while most of the rest of the 51

planet was only covered in a 3 arc-second resolution (around 90 meters). The limitation with the GTOPO30 and SRTM datasets is that they cover continental landmasses only, and SRTM does not cover the Polar Regions and has mountain and desert no data (void) areas. SRTM data, being derived from radar, represents the elevation of the first-reflected surface — quite often tree tops. So, the data are not necessarily representative of the ground surface, but the top of whatever is first encountered by the radar. Submarine elevation (known as bathymetry) data is generated using ship-mounted depth soundings. The SRTM30Plus dataset (used in NASA World Wind) attempts to combine GTOPO30, SRTM and bathymetric data to produce a truly global elevation model. A novel global DEM of postings lower than 12 m and a height accuracy of less than 2 m is expected being generated by the TanDEM-X satellite mission which started in July 2010. The most usual grid (raster) is between 50 and 500 meters. In gravimetry e.g., the primary grid may be 50 m, but is switched to 100 or 500 meters in distances of about 5 or 10 kilometers. Since 2002, the HRS instrument on SPOT 5 has acquired over 100 million square kilometers of stereo pairs used to produce a DTED2 format DEM (with a 30-meter posting) DEM format DTED2 over 50 million km². The radar satellite RADARSAT-2 has been used by MacDonald, Dettwiler and Associates Ltd. to provide DEMs for commercial and military customers. In 2014, acquisitions from radar satellites TerraSAR-X and TanDEM-X will be available in the form of a uniform global coverage with a resolution of 12 meters. Many national mapping agencies produce their own DEMs, often of a higher resolution and quality, but frequently these have to be purchased, and the cost is usually prohibitive to all except public authorities and large corporations. DEMs are often a product of National LIDAR Dataset programs. Free DEMs are also available for Mars: the MEGDR, or Mission Experiment Gridded Data Record, from the Mars Global Surveyor's Mars Orbiter Laser Altimeter (MOLA) instrument; and NASA's Mars Digital Terrain Model (DTM). 3.8 DEM, DSM or DTM 52

There is no common usage of the terms digital elevation model (DEM), digital terrain model (DTM) and digital surface model (DSM) in scientific literature. In the most cases the term digital surface model represents the earth's surface and includes all objects on it. In contrast to a DSM, the digital terrain model represents the bare ground surface without any objects like plants and buildings (see the figure on the right).

Fig.15. Surfaces represented by a Digital Surface Model include buildings and other objects. Digital Terrain Models represent the bare ground. The term Digital Elevation Model is often used as a generic term for DSMs and DTMs, only representing height information without any further definition about the surface. Other definitions equalise the terms DEM and DTM, or define the DEM as a subset of the DTM, which is also representing other morphological elements. There are also definitions which equalise the terms DEM and DSM. In the Web definitions can be found which define the DEM as a digital regularly spaced GRID and a DTM as a real three-dimensional model (TIN).] Most of the data providers (USGS, ERSDAC, CGIAR, Spot Image ) use the term DEM as a generic term for DSMs and DTMs. All datasets which are captured with satellites, airplanes or other flying platforms are originally DSMs (like SRTM or the ASTER GDEM). It is possible to compute a DTM from high resolution DSM datasets with complex algorithms (Li et al., 2005). In the following the term DEM is used as a generic term for DSMs and DTMs.

3.9 Triangulated irregular network

53

A triangulated irregular network (TIN) is a digital data structure used in a geographic information system (GIS) for the representation of a surface. A TIN is a vector-based representation of the physical land surface or sea bottom, made up of irregularly distributed nodes and lines with threedimensional coordinates (x, y, and z) that are arranged in a network of nonoverlapping triangles. TINs are often derived from the elevation data of a rasterized digital elevation model (DEM). An advantage of using a TIN over a raster DEM in mapping and analysis is that the points of a TIN are distributed variably based on an algorithm that determines which points are most necessary to an accurate representation of the terrain. Data input is therefore flexible and fewer points need to be stored than in a raster DEM, with regularly distributed points. A TIN may be less suited than a raster DEM for certain kinds of GIS applications, such as analysis of a surface's slope and aspect. TINs were first invented by Callum Hale whilst studying GIS at University of Hertfordshire. A TIN comprises a triangular network of vertices, known as mass points, with associated coordinates in three dimensions connected by edges to form a triangular tessellation. Threedimensional visualizations are readily created by rendering of the triangular facets. In regions where there is little variation in surface height, the points may be widely spaced whereas in areas of more intense variation in height the point density is increased. A TIN is typically based on a Delaunay triangulation but its utility will be limited by the selection of input data points: well-chosen points will be located so as to capture significant changes in surface form, such as topographical summits, breaks of slope, ridges, valley floors, pits and cols. Although usually associated with 3-dimensional data (x, y, and z) and topography, TINs are also useful for the description and analysis of general horizontal (x and y) distributions and relationships. The first triangulated irregular network program for GIS was written by Randolph Franklin at Simon Fraser University in 1973.

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CHAPTER FOUR 4.1 Introduction: By using different kinds of GIS software we prepare different projects according to our needs. We prepared our project by using ArcGIS 9.3. This software is very well known to the geographers & it’s very easy to use. Description of ArcGIS 9.x : ArcGIS 9 was released in May 2004, which included ArcGIS Server and ArcGIS Engine for developers.[1] The ArcGIS 9 release includes a geoprocessing environment that allows execution of traditional GIS processing tools (such as clipping, overlay, and spatial analysis) interactively or from any scripting language that supports COM standards. Although the most popular of these is Python, others have been used, especially Perl and VBScript. ArcGIS 9 includes a visual programming environment, similar to ERDAS IMAGINE's Model Maker (released in 1994, v8.0.2). The Esri version is called ModelBuilder and as does the ERDAS IMAGINE version allows users to graphically link geoprocessing tools into new tools called models. These models can be executed directly or exported to scripting languages which can then execute in batch mode (launched from a command line), or they can undergo further editing to add branching or looping.On June 26, 2008, Esri released ArcGIS 9.3. The new version of ArcGIS Desktop has new modeling tools and geostatistical error tracking features, while ArcGIS Server has improved performance, and support for role-based security. There also are new JavaScript APIs that can be used to create mashups, and integrated with either Google Maps or Microsoft Virtual Earth.At the 2008 Esri Developers Summit, there was little emphasis on ArcIMS, except for one session on transitioning from ArcIMS to ArcGIS Server-based applications, indicating a change in focus for Esri with ArcGIS 9.3 for web-based mapping applications. In May 2009, Esri released ArcGIS 9.3.1, which improved the performance of dynamic map publishing and introduced better sharing of geographic information.

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4.2 Project-one: Bangladesh Political Map We prepared Bangladesh map showing the division boundary from a supplied map by ArcGIS 9.3. Description of Bangladesh: Bangladesh emerged as an independent and sovereign country on 16 December 1971 following a nine-month War of Liberation. Dhaka (previously spelt Dacca) is its capital. Official name People’s Republic of Bangladesh (Gana Prajatantri Bangladesh) Capital Dhaka. Government Parliamentary form of government, President is head of the State and Prime Minister is head of Government. Geographical location: In south Asia, between 2034 to 2638 north latitude and 8801 to 9241 east longitude. Maximum extension is about 440 km in E-W direction and 760 km in NNWSSE direction. Time; GMT +7.00 hours. Area and Boundaries Area: 147570 sq. km. Boundaries: West Bengal (India) on the west; West Bengal, ASSAM and Meghalaya (all the Indian states) on the north; Indian states of Assam, TRIPURA and Mizoram together with Myanmar on the east; and BAY of BENGAL on the south.

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Map One: Bangladesh political Map 58

4.3 Project –Two ;Dhaka City: We also prepared Dhaka City map showing the division boundary from a supplied map by ArcGIS 9.3. Description of Dhaka city: Dhaka formerly spelled Dacca, named Jahangirnagarduring Mughal era) is the capital of Bangladesh and the principal city of Dhaka Division. Dhaka is a megacity and one of the major cities of South Asia. It is located on the banks of the Buriganga River. Dhaka, along with its metropolitan area, had a population of over 16 million in 2011, making it the largest city in Bangladesh. It is the 9th largest city in the world and also 28th among the most densely populated cities in the world. Dhaka is known as the City of Mosques and with 400,000 cycle rickshaws running on its streets every day, the city is also described as the Rickshaw Capital of the World. Country : Bangladesh Administrative District Dhaka District Establishment 1608 CE Granted city status 1947 Area : • Capital City 360 km2 (140 sq mi) • Water 48.56 km2 (18.75 sq mi) Elevation: 4 m (13.12 ft) Population: (2008)[2] • Capital City 7,000,940 • Density :23,029/km2 (59,640/sq mi) • Metro: 16,623,000(2,011) • Demonym: Dhakaiya or Dhakaite • Literacy rate :62.3% Time zone BST (UTC+6) • Summer (DST) BDST (UTC+7) Postal code 1000 National Calling Code +880 Calling Code 02 Source :

wikipedia.org/wiki/Dhaka

Modern Dhaka is the centre of political, cultural and economic life in Bangladesh. Although its urban infrastructure is the most developed in the country, Dhaka suffers from urban problems such as pollution and overpopulation. In recent decades, Dhaka 59

has seen modernisation of transport, communications and public works. The city is attracting large foreign investments and greater volumes of commerce and trade. It is also experiencing an increasing influx of people from across the nation, this has reportedly made Dhaka the fastest growing city in the world.

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Map two: Dhaka City Map

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4.4 Project–three;Chittagong City: : We also prepared Dhaka City map showing the division boundary from a supplied map by ArcGIS 9.3. Description of Chittagong City Chittagong is the port city with a population of 1,750,000 (1986 est.). It is the commercial and manufacturing center of Bangladesh. Situated on the Karnaphuli river some 19 km (12 mi) from its mouth at the Bay of Bengal, it is the chief port of the country. It provides an extensively developed port facilities for ocean steamers. An ancient city, Chittagong passed from Tippera (Buddhist) dominance to Arakan (Hindu) and then Mogul (Muslim) rule, with periods of re-conquest and re-control. The Portuguese made inroads in the 16th century, and the British gained control in 1760. Industries powered by a hydroelectric plant up the river, use the products of the area-jute, cotton, rice, tea, petroleum (from offshore installations), and bamboo. The bamboo is harvested chiefly from the Chittagong Hill tracts. 13,191 sq km (5,093 sq mi) of rugged, thickly forested land along the Bay of Bengal is inhabited by primitive mountain tribes. Chittagong has a picturesque setting. Its green hills and forests, broad sandy beaches and fine cool climate always attract holiday makers. It combines the hum of a restless seaport with the pleasure of a charming hill-town with its undulating topography. It attracts tourists from around the world. It is surrounded by the bay, the river, and hills high up to 1,200 m (4,000 ft) from sea level. Rainfall averages 2,870 mm annually. Average annual temperature is 26 deg C (78 deg F). PLACES OF INTEREST: Shrine of Bayazid Bostami, World war II Cemetery ,Foy's Lake Ethnological Museum , Court Building ,Patenga and Fouzdarhat 62

Sea Beaches and also Other places of interest include shrine of Shah Amanat, Shahi Jame Mosque, Chandanpura Mosque, Portuguese Arsenal, Port Area, Marine Academy etc.

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Map three: Chittagong City Map

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4.5 Project four ;South America :We also prepared South America Map by using Arc GIS9.3 Software. Here we show different countries by different color.

Description of South America: South America is the southern continent of the Americas, situated entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. It is bordered on the west by the Pacific Ocean and on the north and east by the Atlantic Ocean; North America and the Caribbean Sea lie to the northwest. South America was named in 1580 by cartographers Martin Waldseemüller and Matthias Ringmann after Amerigo Vespucci, who was the first European to suggest that the Americas were not the East Indies, but a New World unknown to Europeans. South America has an area of 17,840,000 square kilometers (6,890,000 sq mi), or almost 3.5% of the Earth's surface. As of 2005, its population was estimated at more than 371,090,000. South America ranks fourth in area (after Asia, Africa, and North America) and fifth in population (after Asia, Africa, Europe, and North America).

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Map four: South America Political Map

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5. Conclusion GIS is a technological field that incorporates geographical features with tabular data in order to map, analyze, and assess real-world problems. The key word to this technology is Geography - this means that some portion of the data is spatial, in other words, data that is in some way referenced to locations on the earth. Coupled with this data is usually tabular data known as attribute data. Attribute data can be generally defined as additional information about each of the spatial features. An example of this would be schools. The actual location of the schools is the spatial data. Additional data such as the school name, level of education taught, student capacity would make up the attribute data. It is the partnership of these two data types that enables GIS to be such an effective problem solving tool through spatial analysis. GIS operates on many levels. On the most basic level, GIS is used as computer cartography, i.e. mapping. The real power in GIS is through using spatial and statistical methods to analyze attribute and geographic information. The end result of the analysis can be derivative information, interpolated information or prioritized information.

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References 1. Hetwood et al. (2003). Geographical Information system Low Price Edition. 2. Geo Atlas, (Latest Digital) 3. What is Arc GIS (9) By ESRI 4. Kumar Pradip (2002). Remote Sensing for Beginner. 5. Bylinsky, Gene, 1989. "Managing with Electronic Maps," Fortune April 24, 237-254. Good review of the state of GIS in mid-1989 from a commercial perspective. 6. Cowen, D.J., 1988. "GIS versus CAD versus DBMS: what are the differences?" Photogrammetric Engineering and Remote Sensing 54:1551-5. Excellent review of the differences in these three traditions. 7. Dueker, K.J., 1987. "Geographic information systems and computer-aided mapping," Journal, American Planning Association 53:383-90. Compares CAD, computer cartography and GIS, conceptually and also at some technical depth. 8. Fisher, P.F., and R. Lindenberg, 1989. "On distinctions among Cartography, Remote Sensing, and Geographic Information Systems," Photogrammetric Engineering and Remote Sensing 55(10):1431-1434. Reviews definitions of each of the three and shows how the disciplines are interrelated. 9. Marble, D.F. et al., 1983. "Geographic information systems and remote sensing," Manual of Remote Sensing. ASPRS/ACSM, Falls Church, VA, 1:923-58. Reviews the various dimensions of the relationship between the two fields. 10. Parent, P. and R. Church, 1987. "Evolution of Geographical Information Systems as Decision Making Tools," Proceedings, GIS '87, pp. 63-71, ASPRS/ACSM, Falls Church, VA. Good review of the history of GIS and its formative influences. 11.

Rhind, D., 1989. "Why GIS?," Arc News, Summer 1989,

Vol 11(3).

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12. http://www.bangla2000.com/bangladesh/Cities/chittagong.s

htm 13. www.wikipedia.com

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