Chapter 3 Input of Geospatial Data


3-1 Required Data Sources for GIS

As data acquisition or data input of geospatial data in digital format is most expensive (about 80% of the total GIS project cost) and procedures are time consuming in GIS, the data sources for data acquisitions should be carefully selected for specific purposes.

The following data sources are widely used.

Analog maps
Topographic maps with contours and other terrain features and thematic maps with respect to defined object classes are digitized by digitizers manually or by scanners semi-automatically. Problems of analog map are lack of availability, out of date, inconsistency in map production time, inaccurate etc.

Aerial photographs
Analytical or digital photogrammetry is rather expensive but the best method for updating

Satellite image
Satellite images or data are available for land use classification, digital elevation model (DEM), updating highway network etc. But the image map scale would be around 1:50,000 to 1:100,000.

High resolution satellite image with ground resolution of 1~3 meters will produce 1:25,000 topomaps in near future.

Ground survey with GPS
Total station together with GPS (Global Positioning System) will modernize the ground survey. It is very accurate but too expensive to cover wide areas.

Reports and publications
Social economic data are usually listed in the reports of statistics and census with respect to administration units.

Figure 3.1 summarizes major data sources for GIS.

Table 3.1 shows method, equipments, accuracy and cost for different data sources.