I get it, this is a rule of thumb that you use. It is better than using a horizontal spacing minium alone.
> I get it, this is a rule of thumb that you use. It is better than using a horizontal spacing minium alone.
You have to consider the site and the curvature of the surface on a cross-section line across it. On the site that was the subject of the OP, the given was 30% average slope transversely and 20% average slope longitudinally. That means if you are going to be getting ground shots at approximately 4 ft. vertical intervals, they will be taken as about 13 ft. average spacing in the direction of 30% slope and about 20 ft. average spacing in the direction of 20% slope. Those will be supplemented by grade breaks and relative high points.
Obviously, if there are lots of grade breaks such as rock ledges and erosional features to be mapped, more points will be needed to add detail to the basic surface mapped. I didn't see any of either in the representative photos.