The New York Public Library (NYPL) has launched a new online tool called the Map Warper, which lets you overlay an old map onto a modern map and digitally rectify the two.
The Map Warper gives you access to more than 20,000 digitized historical maps depicting places around the world. You don’t need to log in to view maps, overlay them, or see already-rectified versions. With an account, you can add your own “control points,” which are points that match up on the old map and the corresponding modern map. A map must have at least three control points to be rectified.
I searched for a map of Cincinnati and found one from 1860.
I created an NYPL account and used the Rectify tab to add a control point where my Ladenkotter third-great-grandparents lived in 1860. The map already had other control points, so I added only the one.
Then I clicked Warp Image, let the Warper finished working, and clicked Preview Rectified Map:
You can zoom in and adjust the transparency. Here’s a closeup of where the Ladenkotters lived, at Abigail (spelled “Abagail” here; it’s now E. 12th) and Spring. It’s just below and to the right of the 9.
You can click the Export tab to download a copy of the original or warped map.
The Map Warper website also has a four-minute video tutorial on using the Warper.