In my area the mapping that the aerial companies provide always seems to lack a statement documenting the basis of elevation and coordinates. No basis of bearings. No published coordinates for the survey control. The work is basically floating in space with no way for a surveyor to tie it back into the ground.
I have seen where engineers design large projects on top of the electronic drawings that the aerial companies provide without a clue as to how it relates to the ground come time to construct the project. Someone knows this information, but god forbid they retire, the files are lost or they go out of business.
Is this common? JRL