13.7 Errors and Fuzziness of Geographic Data and their Influences on GIS Products

a. Errors and Fuzziness of Geographic Data

There are various errors in geographic data with respect to error sources. Of those errors, errors due to the data input method can be avoided by a proper control and check system, while errors due to measurement methods are difficult to avoid completely. It is necessary for users to evaluate the data errors and their influences by sensitivity analysis. Quality control of geographic data in also very essential in GIS.

b. Influences of Errors and Fuzziness

Influences of errors and fuzziness are explained in the following two examples.

(1) Influence on spatial query
Consider a case to check any underground pipe which may be damaged by excavation at a road construction site, as shown in Figure 13.7.1. If only the geometric relationship is checked, there will be no problem as shown in Figure 13.7.1 (a). However, one should consider the uncertainly or error of excavation as well as the pipe, which will make possible the problem as shown in Figure 13.7.1 (b).

(2) Influence on spatial analysis (See Figure 13.7.2)
Consider a case to select suitable land for rice paddy fields by overlaying a slope gradient map, soil map and irrigation areas in Jogjakarta, Indonesia. The area of suitable land will change depending it that there is uncertainly along the boundary of the overlaid areas. If there is 120 meter width of uncertainly along the boundary, the area of suitable land will reduce by about 50 per cent. Thus this uncertainly or error should always be considered.


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