GIS Data Input
The process of encoding the data and writing them to the database is known as Data input. The usefulness of GIS depends upon the creation of a clean digital data. The creation of the data is the most important and the toughest task. For GIS two aspects of data are necessary, the first being the positional aspect and the second one is the associated attributes that give information about the cartographic features in terms of their spatial and non-spatial attributes. This is the advantage of geographic information system over automated cartography. While in automated cartography the non-spatial data mainly relate to color, line, type and symbolisms, in GIS it may also record vegetation types, soil types and land use.
The process of Data input in geographical information system can be described in to the following points:
- Entering the spatial data (digitizing).
- Entering the non-spatial associated attributes.
- Linking the spatial data to the non-spatial data
The resultant database should be free from error, for this there should be proper data verification and checking procedure.
1. Entering the spatial data
There are various methods of entering the data into GIS, which are governed by the features such as application, the available budget and the type of data being input. The type of data encountered is existing map, which includes field sheets and hand flat files and spreadsheets.
All records in flat file or spreadsheet have the same number of “fields”, making it the one of the simplest method for storing data. The individual records have different data in each field and one field serves as a key to locate a particular record. A record can have hundreds of fields. When the number of fields becomes too large a flat file is cumbersome to search.
The structure of the database of the geographical information system also governs the method of data input. In an ideal system user should not have to worry about the form of data processing but it does not happen generally especially in low-budget software.
2. Data sources
The main data source for creating new data are :
- Remotely sensed data (satellite images, aerial photographs)
- Global Positioning System (GPS)
The secondary source of data is Paper Map.
- Remotely sensed data: It is data acquired by a sensor from distance. It includes digital orthophotos and satellites images. These sources of data are raster data but they are useful for vector data input.
- GPS data: GPS data include the horizontal location based on the coordinate system. It is a useful tool for spatial data input.
- Paper maps: All types of hard copy maps constitutes paper maps.
GIS Data Models
The information about the world is stored in GIS in the form of thematic layers, which can be linked together by geography. This simple but powerful concept has helped the world in solving some of its biggest problems such as recording details of planning application and modeling global atmospheric circulations.
This simple layering helps us to organize the complexities of the real world into simple representation and facilitates understanding of natural relations.