Contour interval in TOC

[76mm]

I don't know for sure, but my guess is that determination of the elevation contour is rather simple: I think that there are a limited number of contour elevations available in the map file--take a look. So the higher elevation a map has, the bigger the contour interval has to be.

In other words, lets say there are ten possible contour elevations, and the max elevation on the map is 200 meters; in that case the contour interval is 20 meters (200/10). On the other hand, if the max elevation is 500 meters, then the countour interval is 50 (500/10). This is a bit simplistic, because in fact the internals don't all have to be the same--you can set contour elevations for 0, 20, 40, 60, 80, and 100 meters, then go to 150, 200, etc.

Again, this is just a guess, maybe it was because of what maps are available, etc.