GIS for Starters: Encapsulated basics
Geographic Information System (GIS) is a computer based information system used to digitally represent and analyse various parameters of the globe. Popular use of GIS began in late 1970s and was initiated by Environmental System Research Institute Incorporation (ESRI) of Canada. Much of the credit for the early development of GIS goes to Roger Tomilson, a Canadian GIS specialist.
You may be aware that the earth’s surface not only comprises of spatial attributes, but has non-spatial attributes, which are non-graphic. To put it simply, map features can be quantified in terms of data, such as contours. This is a spatial data.
However when the information provides description about the characteristics of a map and also includes qualitative features, it is categorised as non-spatial. Well, parameters of the globe may have become clear to you, but what does digitally mean? Digitisation is nothing but the conversion of smooth lines, boundaries and so on, into a digital form to allow the computer to read it.
GIS is a computer-assisted system devised to store, retrieve, analyse and display spatial data arranged in a systematic manner. It can also be defined as a computer based system that provides the following sets of capabilities to handle geo-referenced data: –
- Data Input
- Data Management (data storage and retrieval)
- Manipulation and analysis
- Data Output
In some online mapping service, you may have seen satellite imagery. When these images are captured from a satellite or an airplane, they are just plain images, like photographs. But to display these images on a map, they need to be associated with map coordinates. This process is called Geo-Referencing. Once the image is associated with the map coordinates it can be overlaid on top of street maps.
When you type an address or a place name in the search box and in return the map shows a marker at the place. The process of associating an address or a place name with coordinates on the map is called Geo-Coding. In a spatial database this is done as a point layer with name of the place as an attribute to the point location. This is one way of Geo-Coding.
For addresses, the associated coordinates are not saved in a database directly, but computed using a method called linear referencing. The start and end addresses along a line segment are saved and intermediate addresses are interpolated and the coordinates are calculated.
With the knowledge of Geo-Referencing and Geo-Coding, it is now possible to link it to a database, which is nothing but a collection of information about spatial and non-spatial data and their relationship to each other.
The software module is the core of GIS and should be application specific. It must be chosen according to the requirement. The functions of GIS software include storage, analysis and display of geographic information. QGIS – Formerly Quantum GIS, gVSIG, Whitebox GAT and SAGA GIS are some of the well-used free GIS softwares.
There are various techniques used for map creation for further usage in planning for a project. The map creation can be done by either an automated raster to vector creator, using vectorisation packages which convert directly from raster to vector, or manually vectorising, using the scanned images. These digital maps may be products of a survey agency or the result of satellite imagery.
GIS’s broad applications work in tandem with various fields from cadastral mapping, which is a map showing ownership of land-usually large in scale to accurately depict individual landholdings, to utility networks, topographic mapping, thematic cartography, surveying and photogrammetry remote sensing, image processing, computer science, rural and urban planning, earth sciences and geography.
It helps in urban planning, housing, transportation planning, architectural conservation, urban design and managing landscapes. Networking and Disaster Management is also its forte.