GIS (Geographical Information System) – Data Input Techniques

Introduction

GIS stands for Geographical Information System. It refers to a computerized system for data management and serves the purpose of capturing, storing, managing, retrieving, analyzing and displaying spatial information. Spatial information or data refers to any data that is directly connected to a specific location or geographical area.

 data

Fig 1: GIS allows multiple layers of information to be displayed on a single map.

 

GIS uses three types of data:

  1. Raster data (spatial): refers to discrete cells in a rigid row by column format, e.g. satellite or aerial images.
  2. Vector data (spatial): refers to features on the surface of the earth represented by points, lines and polygons.
  3. Attribute data: refers to data that’s attached to the spatial data

Although most GIS systems can display a combination of both types of data, only some GISs can analyse both. Most GIS have several features, including the following:

  • It enables the user to input digitized data that is geographically referenced to a certain location.
  • It enables the user to use relational database management to link certain attributes to each feature.
  • It enables the user to analyze relationships between several geographic features with the help of a vast range of spatial operations and features.
  • It enables the user to produce high quality images on color monitors or plotters.

Data Input Techniques

data2

Fig 2: Data Input Techniques in a common GIS

A common GIS uses several modes of inputting data to the GIS. The choice of mode depends on application, available budget, type and complexity of data.

There are 4 basic methods of data input (as shown in the Fig. 2):

  1. Manual digitizing:

A digitizer refers to an electronic device that includes a table on which a map or drawing is placed. The user traces out the spatial features using a magnetic pen which sends the data collected to a computer. This data is then registered to a coordinate system based on the coordinates entered by the user when starting the digitizing process.

Digitizing can be carried out in the following modes:

  • Point mode: single points are recorded at one time.
  • Stream mode: one point each is collected at regular breaks of time and distance.
  • On-screen mode: when the digitized line-work is displayed on a graphics terminal while being digitized.

Digitizing can be very time-consuming and so expensive.  However, if the digitized maps are managed correctly they can be used over-and-over, and so for this reason become cost effective. Digitizing can take time to learn and to master.

  1. Automatic scanning:

This is where a scanner captures the spatial data automatically. Scanning devices can capture spatial data at a very high speed. However, these scanners are often quite expensive and are usually unable to recognize text and symbols. Scanned data also requires a large amount of editing, which is done manually, therefore it is more time consuming.

Since scanners are expensive to afford, it often gets difficult to send hard copy maps to a scanning device. Most companies use scanners of others to obtain their data. If the hard copy maps are of low quality, it is often difficult for a scanner to produce high quality results. In addition, a single map can have a limited number of spatial features making it even more time consuming and hard to afford.

Automatic scanning is proved to beneficial only if the hard copy maps are of high quality, clean, neat and less cluttered. Latest research has also highlighted the fact that automatic scanning has great potential in the upcoming years.

  1. Entry of coordinates via coordinate geometry:

Coordinate geometry is a means of entering explicit measurements of features from some known monument. This data is entered based on surveys. However, it is said to be very expensive in terms of capital and labor. It is hardly used for natural resource applications in GIS. It is useful for producing detailed images of property.

  1. Conversion of existing digital data:

This involves the process of converting data from CAD systems to a GIS or topological form. Most software vendors of GIS provide a data exchange format where users can write their own data conversion routes.

The GPS is also another means of data conversion where spatial features are represented in 3D maps to direct routes to reach a certain location.

Conclusion

GIS uses a variety of methods to input data to its software. The selection of these methods varies depending on the volume and type of data being input. Each method has its own advantages and disadvantages which clearly differentiate one from the other. Most important factors to consider while choosing a data input method include cost, time consumption, speed and quality. It is up to the user to choose any mode of data input based on his requirements. However, as technology expands, newer and better ways of GIS data input methods will be introduced.

 

 

References:

http://bgis.sanbi.org/gis-primer/page_25.htm
http://nerrs.noaa.gov/doc/siteprofile/acebasin/html/gis_data/gisint2.htm
http://www.amesremote.com/section4.htm
http://education.nationalgeographic.com/education/encyclopedia/geographic-information-system-gis/?ar_a=1

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