Geographic Information Systems: An Introduction, 3rd Edition

9.1 Introduction

At the outset, sources of data used in GISs may be (Figure 9.1):

• In various digital forms: vector, raster, databases, spreadsheet tables, satellite data, and so on
• Nondigital graphics, such as conventional maps, photographs, sketches, schematic diagrams, and the like
• Conventional documents in registers and files
• Compilations in scientific reports
• Collections of survey measurements expressed in coordinates or other units

The data sources for a comprehensive GIS are probably more numerous and of greater variety than for most other information systems. GIS is a true mixed-data system. Most often, the data mix makes for a lively system. Although most of the problems associated with collecting data for GIS uses were identified by the mid-1970s, data collection remains the most expensive and time-consuming aspect of setting up a major GIS facility. Experience indicates that data collection accounts for 60 to 80% of the total cost (time and money) of a fully operational GIS, whereas the purchase of equipment accounts for not more than 10 to 30%. Other costs include training, development, and administration. As shown in Figure 9.2, the costs of data collection are dominant even when spread over an implementation period of several years.

There are four methods of producing digital map data:

1. Digitizing existing maps with a digitizer
2. Scanning existing maps
3. Digital photogrammetric map production
4. Entry of computed coordinates from field measurements

The first three methods, ...