Database creation is most important, expensive and time taking part of any GIS project. Data input is the operation of encoding the data and writing them to the database. The creation of a clean digital data is a most important and complex task upon which the usefulness of the GIS depends.
Two aspects of the data need to be considered separately for geographical information system, these are first the positional or/ and second the associated attributes that records what the cartographic features in terms of their spatial and non-spatial attributes that is the main distinguishing criterion between automated cartography ( where the non-spatial data relate mainly to color, line, type, symbolisms etc.) and geographical information processing ( where the non-spatial data may record land use, vegetation types, soil types etc.)
In a geographical information system data input can be described in to following point: -
- Entering the spatial data (digitizing).
- Entering the non-spatial associated attributes.
- Linking the spatial data to the non-spatial data.
At each stage there should be necessary a proper data verification and checking procedures to ensure that the resultant database is as free as possible from error.
ENTERING THE SPATIAL DATA
There is no single method of entering the spatial data to a GIS rather, there are several mutually compatible methods that can be used singly or in combination. Largely the application, the available budget and the type of data being input govern the choice of method. The type of data encountered is existing map; including field sheets and hand flat files & spreadsheets.
A flat file or spreadsheet is a simple method for storing data. All records in this database have the same number of �fields�. Individual records have different data in each field with one field serving as a key to locate a particular record. For example, in parcel mapping house number may be the key field in a record of name, plot size, number of floors, number of families etc. There can be hundreds of fields associated with the record. When the number of fields becomes lengthy a flat file is cumbersome to search.
The actual methods of data input are also dependent on the structure of the database of the geographical information system. Although in an ideal system the user should not have to worry about whether the data are stored and processed in raster or vector form, such flexibility is still far from generally available, particularly in low �budget soft wares.
DATA SOURCES: -
Data sources for creating new data include remotely sensed data (Satellite images, Aerial photographs), GPS (Global Positioning System) data, paper maps and so on. Remotely sensed data and GPS data are the primary data sources and paper maps are secondary data sources.
- Remotely sensed data:- Remotely sensed data , such as digital orthophotos and satellites images, are data acquired by a sensor from distance, Remotely sensed data are raster data but they are useful for vector data input. Digital orthophotos are digitized aerial photographs that have been differentially rectified or corrected to remove image displacements.
- GPS Data: - GPS data include the horizontal location based on the geographic grid or a coordinate system. It has become a useful tool for spatial data input.
- Paper Maps:- It include all types of hard copy maps.
