When the maps were still owned by Sanborn, they were subscribed to by libraries and then available to their cardholders. Although expensive to the libraries, it was free to the rest of us. Now a few libraries subscribe to some of them, but the maps have mostly all been acquired by
Environmental Data Resources, Inc. in Milford, CT, 800.352.0050 and can be purchased though them. I think they are about $345 for all of the historical maps of a particular site. I assume environmental engineers are their best customers when preparing phase one reports.
The good news is that they can be obtained, but the bad news is that this is prohibitive pricing if you are merely fishing around exploring various sites for historical development information, which I used to do frequently. This is hugely valuable information about the development of our cities (including many, many small towns) and unfortunately seems to be a lost resource for us.
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Allen Casey AIA
Casey Architecture
Springfield MO
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