A friend of mine who is well versed in urban planning and such mentioned Fire Insurance Plans to me a while back.
If anyone is unfamiliar with the term, Fire Insurance plans provide detailed information about buildings and neighbourhoods. They usually date back, decades or even centuries. Information like the character of the outside and inside construction of buildings, building heights, occupancy or use of individual or groups of buildings, street widths, property lines etc can all be found within a Fire Insurance plan.
Most universities or public libraries have Fire Insurance plans available to the public either online or at the library itself.
While of course information and landscape has changed I found them interesting and potentially useful to urban exploring. Even for those who love draining can find information on tunnel systems within a Fire Insurance plan. It may also give historic insight to properties that remain.
University of Waterloo has a pretty good library of Fire Insurance plans pertaining to the area and much of Southwestern Ontario. https://uwaterloo....re-insurance-plans