In Mayland, one can download copies of the tax map, which shows all current
property boundaries. These are available in every state, I'm sure, although
sometimes only in paper copies at the Court House.
Through some work, I've managed to scale and rotate them correctly and I use
them as the image in DeedMapper.
These are particularly useful, since many property lines have not changed
since the 1600's. When I've mapped an old deed, I often find its location by
fitting it into the current tax map, much like a child's puzzle where there are
carved out shapes on a board.
Please write me if you want to hear more about this, including some samples.