I digitized contour lines from topographic maps and created a DEM. With the DEM, I estimated the boundary of a catchment area. Estimated positional accuracy of topographic maps is RMSE = 65 m, with a systematic bias towards East. Using an affine transformation (R-package vec2dtransf), I shifted the data towards West. The RMSE of the affine transformation is 30 m.
Visual check of the boundary using satellite images suggests that its actual position is more accurate than the former. However, I understand that there still is an uncertainty about the correct position and shape of the boundary.
I will use the estimated boundary to limit the area were to make predictions of soil properties. But I want to be more confident that predictions cover the real area of the catchment. Thus, I am planning to increase the area adding a buffer equal to the RMSE of the affine transformation (30 m).
I like to know if this approach is correct and if I am missing something.