What Is Geographical Information System

Published Date: 02 Nov 2017

Geographic information system a computer‐based. information system that enables capture, modeling, storage, retrieval, sharing, manipulation, and presentation of geographically referenced data.

Geographical Information System consist with following components...

Computer hardware

Set of application software modules

Skilled people to manage it

Application which uses GIS

Geospatial data

http://webapp1.dlib.indiana.edu/cgi-bin/virtcdlib/index.cgi/4302870/FID1/html/images/gisparts.gif

Sri Lankan survey department GIS unit

Survey department provides the map data which is the base for any Geographic Information System in the Sri Lanka. The modern GIS is a computerized geographic database system. The modern GIS is a geographical database with tools for data analysis and data presentation. A GIS is a tool we use to help us to store and manipulate large datasets and to perform complex operations that would take a human a long time. Algorithms and storage techniques are used for this purpose. Data capturing from an aerial photographs has been doing digitally since 1992 that can be directly feed to any sort of Geographic Information System. However, one should bear in mind that the scale of the spatial information as well as the accuracy required. The Geographic Information System technology in conjunction with remote sensing and photogrammetric can be used to identify hazards. Land hazard prone areas, flood prone areas, seismic faults can be identified by scientists using Geographic Information System to analyze satellite data, air photos and field surveys data. Once the hazards have been identified, their representation can be stored conveniently in a GIS databases. In addition, new hazard layers can be generated within a GIS by combining hazard layers for example , Landslide hazard layer can be generated by overlaying elevation, surface geology, water table and landslide inventory data.

The need for Geographical Information

As the population increases in what happens to our natural resources? of course they deplete. So there is a demand on the Earth’s resources of land, air, water and raw materials. With the realization that better management is required of limited resources, people have become more organized. Complex social and economic patterns have evolved. Human beings have understood the need for better sharing of resources between humans as well as for all forms of life. So we must learn to make the most of our resources. It must be mentioned here that it is not only the natural resources but also the changes brought about through social and technological advances also needs to be monitored constantly. How do we set about doing all this? First we need to understand the spatial & temporal patterns of resources and also spatial & temporal processes governing their availability. Let us see what this means. We need to know exactly where the resources are located (spatial data). Data needs to be monitored continuously. For this reason, we need to obtain data of a resource or a phenomenon at different times (temporal data). The temporal process for obtaining rainfall data can be on a daily basis. The temporal process for obtaining population data can be once in ten years. GIS is all about how we record the information in order to be able to retrieve the data when required.

Geographical Information Supports vivid applications going on Sri Lanka

Operational Applications:

Utilities management

Telecommunication

Transportation

Emergency management

Land administration

Urban planning

Military applications

Library management

Social & Environmental applications:

Local, National & Global applications

Healthcare applications

Politics

Monitoring land-use

Environmental monitoring and assessment

Geographical Information

For everybody to read and understand records or maps it was necessary to have units of geographic information. We can use real symbols and attributes to represent real world objects.

Symbols

Point: Schools, hospitals etc.

Lines: Contours, streams, roads etc.

Polygons: Land use, Provinces, districts etc.

Attributes:

These any other data relevant to that particular spatial data as indicated by the symbol. They are the non-geographic characteristics of the geographical entities (spatial information) in a GIS.

Data capture, data input & verification:

Geographic data is the information about the earth’s surface and features on it. Feeding the data or the information into the system is referred to as data capture. Before we see how we can capture data, let us first understand what geographic data really is and the different forms in which this data can be represented.

Vector data

In the vector format, positions are stored in the form of coordinates. (x,y and sometimes z). A point is described by a single x,y coordinate pair and by its name or label. Although a line is actually an infinite set of points, in practice a line is described by straight-line segments, each segment described by a set of coordinate pairs and of course the name or label. An area also called a polygon, is described by a set of coordinate pairs and by its name or label with the difference that the coordinate pairs at the beginning and the end are the same. A vector format represents the location and shape of features and boundaries precisely provided they are accurate at the point of input.

Raster data

The grid-based format generalizes map features as cells or pixels in a grid matrix. The space is defined by a matrix of points or cells organized into rows and columns. If the rows and columns are numbered, the position of each element can be specified by the column and row numbers. These can be linked to coordinate positions through the introduction of a coordinate system. Each cell has an attribute value (a number) that represents a geographical phenomenon or nominal data such as elevation, land use class etc. The fineness of the grid or in other words the size of the cells in the grid matrix, will determine the level of detail in which map features can be represented.

Operations of a GIS

We can observe the following operations using a GIS software,

Point-in polygon queries: When we click the mouse while inside the region of a computerized map, the program must perform a point-in-polygon test to find out what you are interested in.

Proximity-based queries: For example if w need to know the number of schools lying within a certain distance from a point, you can create a buffer zone to obtain the result.

Network queries: To get at the optimal routes for travel, water pipeline or any other. It can also be network load queries where you try to find out the response of a drainage system to heavy rainfall etc.

Thematic maps: These are methods of presenting information for quick and easy reference. Just having a table of numbers may very often not indicate some important point.

At national level we need to have data about different areas in order to decide on priority requirements. The different data figures for different items such as the number of doctors serving each district, the number of school going children with the number of schools in a district and so on can be reflected much better using maps. Townships are complicated complexes where a data base is required for many types of information. Location of streets, houses, culverts, electricity, water & sewage line information are just a few.

Using these information one can establish a GIS that suitable for the specific requirement. The GIS can be used for the analysis to determine landslide hazard prone areas as well as in the printing of such maps. Hazard and vulnerability data which is both spatial and non-spatial in nature can be stored in GIS databases. Finally, by displaying the potential damages that can be caused by natural hazards, GIS helps planners and insures to take preventive actions.

Collection of data from aerial photographs in digitally or digital format manner has been having to the Survey Department in year 1992. At present department is enriched with ten analytical plotters, one digital workstation and 7.2 micron high resolution photo scanner. It provides facility to produce high quality, orthorectified, and geo-referenced aerial photographs quickly, easily and cheaply

The Survey Department being the national Surveying & Mapping organization that provides geo-spatial data to other institutions and individuals for their needs. Since 1992, 1:10,000 topographic map series has been produced using photogrammetric method. Data are available in digital form for all areas to be developed. In 1993 the geodetic control network of Sri Lanka was upgraded by using precise baselines measured using global positioning system. The transformation parameter were computed from the local datum called Everest 1830 to global datum called WGS84. Hence Global Positioning System receivers can be used to obtain the national grid system centimeter level accuracy.