Data input is one of the first steps in many GIS applications. It is an important aspect of any GIS application. There are several methods for entering data into a GIS. In this article, a few important data input techniques are discussed.
The process of getting the data into a computer is termed “data encoding” in GIS. A data stream is the combined process of data encoding and data editing. While working on an application, GIS must accept different types of data produced from different sources.
Multiple data input techniques are developed since a single method cannot be used for all types of data. Some of the important techniques are as follows: 1) keyboard entry 2) Manual digitizing 3) Automatic digitizing 4) Scanning
Keyboard input technique
Data entry through keyboard is one of the simplest techniques to input GIS data for an application. This method is also called as key encoding. Data is entered into GIS using keyboard directly at the computer terminal.
This technique is mainly used for the entry of attribute data which is available in the non-digital format. However, this technique can also be used for digitization. The attributes are linked to digitized features using common identification codes. The coordinates of entities such as points, lines and polygons can be entered using keyboard.
This method generally produces very precise information compared to other techniques. However, this method is not very convenient when there is large amount of data.
This is the most common method of data entry in GIS. Digitization is the process where the spatial features on the non-digital map are converted into digital format. Different digital features such as point, line and polygon are used for the construction of map. Complex geometrical maps can be formed by combining points and lines.
Advantages of digitizing the map:
Attribute entry and selection can be simultaneously done while performing digitizing. Further, digitizing is the simplest way for digitizing more amount of data.
Problems with digitization:
The accuracy of output depends on the quality of input map used as source. Selection of ground control points is another important aspect, that can trigger uncertainties in the output map. Experience of the person, scale of the map etc., can affect the precision and accuracy of the digitized map.
There exist different types of digitization such as heads up digitization and heads down digitization.
There are GIS packages, that can automatically detect the topographic feature boundaries of input document. Further, there are devices such as digitizing pens using which various features are scanned quickly to digitize the maps. This type of digitizing is also called as heads down digitization. However, the output requires extensive cleaning for removal of unnecessary points.
Scanning can be used for producing raster data. Various types of scanners are used for converting map documents into digital format, which can be used directly in GIS. These documents may be used as source documents for digitization purpose as well.