How does the size of Baltimore city in the early 19th century compare with how the city looks today?
A new project from the University of Richmond’s Digital Scholarship Lab shows a map of Baltimore in 1801 that overlays a map of the current city limits.
View the map here.
The Atlantic Cities has more:

Just before the holidays, the University of Richmond’s Digital Scholarship Lab unveiled an ambitious project bringing the entire [Atlas of the Historical Geography of the United States] online, complete with the kind of digital enhancements that were never available in [Charles O.] Paullin and [John K.] Wright’s day. The old paper maps have been geo-rectified so that they can be viewed atop digital maps.

There are similar then-and-now maps for Philadelphia, New York City, Boston and other cities.
Read more about the project at the Atlantic Cities.