In this article we will discuss about:- 1. Introduction to Geographic Information System (GIS) 2. Capabilities of GIS 3. Components of GIS 4. GIS Operations 5. GIS Application.
Contents:
- Introduction to Geographic Information System (GIS)
- Capabilities of GIS
- Components of GIS
- GIS Operations
- GIS Application
1. Introduction to Geographic Information System (GIS):
Maps depicting different geographical features are required for a wide variety of purposes such as navigation, locating engineering structures, calculation of distances, areas or other such entities. In projects relating to natural resources management, the maps of an area showing different features like topography, land use/land cover, soil types, land slope, geomorphology, geology, etc. are needed.
Topographical maps are considered as general purpose because they can be interpreted for different purposes, but the maps of land use/land cover, soil types, rainfall, population, etc. are made for limited purposes.
These specific-purpose maps are usually known as ‘thematic maps’ because they contain information about a single subject or theme. Maps can be prepared using aerial photographs, remote sensing techniques, land surveying and cartographic methods.
Different thematic maps are overlaid in order to compare their features in relation to each other as well as to create a composite map. The traditional technique to overlay maps is the use of an illuminated table, which is not only time consuming but also the maps of different scales are difficult to be accommodated.
With the availability of digital computers, paper maps can be converted into a digital format by electronic devices known as ‘digitizers’ or ‘scanners’; the latter is preferred to avoid human errors and minimize time and labour.
Geographical data are digitized or scanned electronically into the computer database. Once a paper map is converted into the digital format, its alteration into any desired format is possible on the computer for the purpose of analysis.
The geographical data or geographically referenced data describe both the location and characteristics of spatial features on the earth’s surface (e.g., rainfall, temperature, evapotranspiration, rivers, canals, elevation, railways, roads, buildings, forests, water bodies, etc.).
Thus, the geographical data have two components namely ‘spatial data’ (relating to the geometry of spatial features/phenomena) and ‘attribute data’ (non-graphic information associated with a point, line or area element such as cost, color, pH, width, depth, thickness, etc.). In a Geographic Information System (GIS), real-world spatial features are represented by points, lines, or polygons.
2. Capabilities of GIS:
The Geographic Information System (GIS) goes further than simply storing the geographical data in the computer. In a GIS, new maps can be generated precisely by easily integrating several layers of geographical data.
A GIS facilitates the creation of a database containing multiple information layers (often called ‘thematic layers’) that can be manipulated to evaluate relationships among the selected elements in different layers under diverse conditions according to the need of users.
In a GIS, different maps can be combined efficiently and the process is known as ‘overlaying’ or ‘map overlaying’. For example, maps of soil types, forests, grasslands, etc. can be overlaid with those of infrastructure (like roads or buildings), population density, climate, and economic and social data.
Thus, a new map with its own spatial relationships can be produced according to user needs. In project planning, several alternatives and possible consequences of a particular action can conveniently be examined using a GIS. In a GIS, the information obtained from satellite imagery can be integrated into other data sets. After getting new data sets, these data can be integrated with the available information to form a revised GIS database.
The following definitions of GIS explain its capabilities:
(i) GIS is a computer system capable of assembling, storing, manipulating and displaying geographically referenced information.
(ii) GIS is a computer system for capturing, storing, querying, analyzing, and displaying geographical data.
Spatial data analysis is a multidisciplinary activity concerning subjects like geography, hydrology, water resources, earth sciences and habitat planning. Spatial datasets are generally heterogeneous, consisting of data on soils, rainfall, infiltration, land use, topography, forest cover, administrative boundaries, population distribution, etc.
They are often available at different scales, in different coordinate systems, and have various levels of accuracy and aerial coverage. GIS facilitates management and analysis of such large volumes of data.
Some of the standard operations for which GIS is being used are – integrating maps made at different scales; overlaying different types of maps which show different attributes; identifying required areas within a given distance from specific features like roads, rivers or human habitations; statistical analysis of features like calculation of areas of water bodies, forests etc., and lengths of rivers, roads or canals.
Thus, GIS has emerged as a powerful and sophisticated tool for managing vast amounts of geographical data and for making decisions in several areas including engineering and environmental fields.
3. Components of GIS:
A GIS consists of four integrated components, which are as follows:
(i) Data and databases,
(ii) Hardware,
(iii) Software, and
(iv) Users.
Data and Databases:
The data and databases in a GIS are essentially of two kinds, viz., maps showing the specific characteristics of a location and attribute data in the form of written text, tables and lists. In a GIS, vectors and raster (grids) are the two basic geo-coding systems, which are known as ‘data models’ or ‘data structures’ for a GIS. A vector system stores data as coordinates e.g., a uniform area is bounded by a set of straight line segments called vectors.
On the other hand, a raster (or grid) system is a cell-based system in which a map is represented as an array of rectangular or square cells. Satellite images are digital geographic data in the raster form.
An advantage of the vector-based system is that it shows thematic maps precisely and requires less computer storage space compared to the raster system. Although storage requirements are larger in the raster system, processing is simpler and compatible with other digital images.
Hardware:
The computer hardware for operating a GIS should be able to support the data input, output, storage, retrieval, display and analysis.
The following are the essential elements of the hardware required for a GIS operation:
1. A processor with sufficient power to run the selected software,
2. Sufficient computer memory for storing large volumes of data,
3. A high resolution colour graphics screen, and
4. Data input and output devices (i.e., keyboard, mouse, digitizer, scanners, plotters and printers).
Software:
Software is either developed or selected to execute the GIS operation on the computer. At present, several GIS software packages are readily available, each offering different levels of functionality.
Some of the commonly used GIS software packages are:
While all the above-mentioned software packages have some common features, some of them have certain special capabilities which can be understood by a closer study of the particular software.
At present, the software GRASS and a certain version of ILWIS are free of cost. The capabilities of the selected GIS software package should be clearly understood before it is used extensively.
4. GIS Operations:
A general understanding of the problem to which the GIS is going to be used and the available information should be understood first.
In applying GIS to a specific problem, the following operations are generally followed:
i. Spatial data input,
ii. Attribute data management,
iii. Data display,
iv. Data exploration,
v. Data analysis, and
vi. GIS modeling.
Database construction is the fundamental part of any GIS project. It can be constructed using existing (in situ measurements, paper maps or aerial photographs) and new data obtained from satellite imagery or GPS (Global Positioning System) data.
GPS is a set of satellites in geostationary earth orbits which are widely used these days to help determine geographic location anywhere on the earth by means of portable electronic receivers.
The satellite data being digital in nature, can be interpreted and analyzed using various available image-processing software packages. It is easy to feed such information into the GIS environment for integration with other types of data.
A wide range of image analysis software packages with GIS facilities are also commercially available such as Arclnfo GRID, IDRISI and GRASS. Also, GPS measurements are available in a format that can be directly input to a GIS database.
Thus, the remote sensing techniques (and GPS) along with a GIS aid to collect, analyze and interpret the data rapidly on a large scale. Since only digital data can be handled by a GIS, paper maps need to be either digitized using a digitizer or scanned using a scanner. Digitizing errors are removed by data editing. The digitized or scanned maps must be converted to real-world coordinates by using a set of control points with known real-world coordinates (called ‘geometric transformation’).
Following the spatial data input, non-spatial data or attribute data (i.e., features of a spatial entity; for example, the attributes of a spatial entity ‘road’ could be type and width of the road, type of surface, construction method, date of construction, etc.) must be entered and verified in order to complete the database construction.
Since remote sensing images and aerial photographs are nonselective in nature (i.e., direct extraction of data is not possible), they have to be interpreted or analyzed before useful data can be added to the GIS database.
The UTM grid system is widely adopted for most remote sensing images; topographic map preparation and natural resource database development because it allows precise measurement using the metric system of measurement. In a GIS, the data are displayed through maps, tables and charts. As a visual tool, maps are the most effective in communicating spatial data.
Data exploration means data-centered query and analysis. It can be a GIS operation by itself or a precursor to formal data analysis. Data query allows the GIS user to examine general trends in the data, to have a clear look at data subsets and to explore possible relationships between data sets. Thus, the purpose of data exploration is to better understand the data under study and to help formulate research questions and hypotheses.
Data analysis in a GIS is closely related to the data models. As mentioned earlier, the basic data models are vector and raster, each having its own sets of analytical functions. Although some GIS concepts such as map overlay and buffering (i.e., process of creating a zone of specified width around a point, line or area entity) are the same for vector and raster data, the operational procedures differ.
GIS can also be used in the process of developing models (analytical or numerical) using spatial data. A very useful GIS operation for modeling is the ‘map overlay’ which helps in extracting new data or information for modeling.
GIS applications in hydrology and water resources management are essentially in the modeling context. Various applications of GIS to hydrology (including hydrological modeling) are outlined in Singh and Fiorentino (1996) and the use of GIS in groundwater studies including modeling is discussed in Jha and Peiffer (2006).
5. GIS Application:
Since the beginning, GIS has been important in natural resources management such as land use planning, water resources management, forest management, riparian zone monitoring, and natural hazard assessment.
In recent years, GIS has been used in emergency planning, market analysis, facilities (like electricity, gas and water distribution systems) management, flight management and transportation planning.
The spatial nature of data associated with land and water resources is the most important factor contributing to the complexity of data management. With its ability to combine a variety of and voluminous data into an easily understood format as well as to effectively analyze, model and display, GIS can drastically change the way engineers handle real-world water resources problems.
Integration of GIS with emerging technologies such as Global Positioning System (GPS) and Internet has introduced several new applications, and the use of GIS as a decision-support system is gradually becoming popular.
The newly developed concept of ‘precision agriculture’ (or precision farming) is also heavily dependent on GPS and GIS technologies. Thus, GIS today serves as a valuable and indispensable tool for land- and water-related environmental planning and management.
Generally, GIS applications can be grouped under the following categories:
(1) Calculation of areas and lengths on the GIS-generated maps.
(2) Scale and projection changes as well as coordinate rotation and translation.
(3) Display of geographical data.
(4) Reclassification of thematic attributes in map features.
(5) Map overlaying using different thematic layers.
(6) Detection and display of spatial relationships using empirical and statistical models.
(7) Database management, exploratory data analysis, and data visualization for simulation modeling.
In land and water management engineering, some of the studies where GIS is being used are as follows:
(1) Inventory and mapping of land resources.
(2) Land evaluation and rural planning.
(3) Analysis of land use/land cover changes and climate change.
(4) Watershed delineation and hydrological modeling.
(5) Inventory and mapping of forest resources.
(6) Inventory and mapping of water bodies and water quality/quantity.
(7) Assessment of flood, drought, erosion and pollution hazards and damages.
(8) Evaluation and management of groundwater resources.
(9) Mapping of cropping patterns and crop yield projections.
(10) Command area development and management.
(11) Environmental impact assessment of human activities.
(12) Weather and climate modeling and prediction.
Some of these applications are elaborated in the following:
1. Land Use/Land Cover Change Analysis:
For effective land use and management, the present land use information is essential. GIS-supported remote sensing data have proved to be very useful in monitoring the land use and land cover changes as well as in updating the existing land use maps.
The land use maps can be overlaid with maps of soil type, topographic slope, water availability, etc. and modeled in a GIS to develop optimal land use plans.
Once the basic information about physical characteristics of land and related climatic factors are available, this information can be used for several other studies such as land suitability analysis, land degradation due to different forms of soil erosion, deterioration of water quality due to point and non- point sources of pollution, impacts of land use changes on land and water resources, etc.
The scope of GIS for soil erosion studies include apart from overlaying exercises, analyzing the effects of topography, climatic factors and environmental factors on erosion processes.
2. Forest Resource Inventory and Mapping:
The aerial extent of forest cover, change of forest cover with time, forest ecosystem studies, strategies for forest protection, etc. can conveniently be studied using integrated remote sensing and GIS techniques. Such studies are also suitable for developing strategies for forest development along with other land management practices.
3. Watershed Delineation and Management:
Once a GIS database is developed for a region with all the land, soil, vegetation and population information, it can conveniently be used for watershed development in that region. Depending on the area, watersheds could be delineated.
Using the information in the GIS, it is also possible to estimate runoff and sediment/nutrient losses from watersheds. Best management practices (BMPs) for a watershed could also be suggested based on the hydrological modeling using integrated remote sensing and GIS techniques, even though ground truthing (i.e., verification) is needed before implementing the suggested practices.
4. Groundwater Development and Management:
In groundwater studies, GIS is useful for handling different types of spatial information required for evaluating groundwater resources as well as developing groundwater models. GIS for surface-water modeling has been more prevalent than for groundwater modeling because the available standardized GIS coverages (thematic maps) are primarily of the land surface; few standardized coverages of hydrogeologic properties are available.
Also, GIS is useful in depicting groundwater basins (i.e., aquifer systems), flow and recharge patterns in a basin, and basin- wide water quantity and quality variations.
These thematic maps could be overlaid with human settlements for deciding drinking water availabilities and when considered with agricultural lands, water supply to cropped areas.
A detailed survey of literature revealed six major areas of remote sensing and GIS applications in groundwater hydrology –
(i) Exploration and assessment of groundwater resources,
(ii) Selection of artificial recharge sites,
(iii) GIS-based subsurface flow and pollution modeling,
(iv) Groundwater vulnerability assessment and protection planning,
(v) Estimation of natural recharge distribution, and
(vi) Hydrogeologic data analysis and process monitoring.
GIS is essentially a computer-based technology and hence, fundamental knowledge of the use of computers and related accessories is required for the efficient use of a GIS. Application of GIS is more useful when it is used along with the images obtained by remote sensing techniques.
Therefore, a proper knowledge of image interpretation techniques is also necessary for GIS users. The accuracy and effectiveness of GIS is dependent on the quality and adequacy of data required for a particular study.