There is a 1937 property atlas of Providence by G. M. Hopkins which shows on one of its plates the neighborhood of Lovecraft's last residence and its relation to other structures. If someone with a digital camera can get a shot of it, this would be something putting on a website. There are also similar atlases for Brooklyn and Manhattan. Both CAS and REH lived in more rural areas which generally didn't have that level of mapping, but county level maps did exist and people in Texas and California might try county historical societies and see just how detailed such maps are. Not that E. R. Burroughs is central to this list, but he bought up a ranch and later sold off portions of it. Records at various times should exist.

J. B. Post