How does the aerial photo scale and the digitizing scale influence the river bank measurement error in GIS?
Information on the magnitude of the river bank measurement error is necessary to assess the magnitude of channel changes that may be identified during an analysis.
In this paper, the impact of the aerial photo scale and the measurement scale in the GIS software on the magnitude of the digitization (identification) error of a river channel bank was analysed. Repeat digitization of the same channel bank carried out in aerial photographs differing in the scale (1:7,500–1:30,000) with different measurement scales (1:1,000–1:10,000) used on each of them, showed that increasing the scale used for digitizing in the GIS software decreased the magnitude of digitization errors much more than similar increasing the aerial photo scale. The results of the analysis show that the selection of an appropriate digitizing scale in GIS software is an important factor affecting measurement error. The discussion of the results indicates that in some cases the calculation of the digitization error based on the aerial photo scale or the arbitrarily assumed error value may be higher than the real error which has occurred during digitization. The results obtained showed that the product of 0.25 mm and the scale used for digitizing in GIS can be a good approximation of the digitizing error which occurred in the aerial photos taken at the scale range of 1:7,500–1:30,000.