The purpose is to explore the effect of the spatial distribution of ground control points (GCPs) on the accuracy of imagery rectification. Both area-distributed and linearly distributed GCPs were used to rectify a Landsat TM image of a coastal zone. Rectification accuracy was checked against 99 independent points over the intertidal mudflats with no ground control. Results indicate that the root-mean-square error of residuals over these areas is several times larger than its GCPs-measured counterpart. If the GCPs are spatially dispersed over an area, residuals fluctuate but increase steadily with distance to the source of control in easting (R 2= 0.827). In northing they fluctuate around 150 m until 15 km, beyond which they rise steadily at a small range of fluctuation. These residuals are less predictable from distance to the source of control than in easting (R 2=0.517). If the GCPs are distributed along a control line, residuals rise with distance to it linearly and predictably (R 2=0.877) in the direction perpendicular to it. In a direction parallel to it, the distance has little impact on rectification residuals.
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