An interest in genealogy inevitably leads to other interests: whether Civil War re-enactment, tin-type photography, or, as in my case, cartography. I have found, both on- and off-line, dozens of historical maps of my corner of Maine, each of which adds something to my understanding of the region. Historical USGS Maps of New England and New York provides free topographical maps (often more than one for a particular area), while Old Maps of New England, New York & Pennsylania sells matted reproductions of 19th-century town maps which show exactly where each resident lived, where he went to church, and where his children went to school. The map collection at American Memory includes panoramic maps of many American towns.
And then there is the David Rumsey Historical Map Collection, which "has over 11,000 maps online."
The collection focuses on rare 18th and 19th century North and South America maps and other cartographic materials. Historic maps of the World, Europe, Asia and Africa are also represented. Collection categories include antique atlas, globe, school geography, maritime chart, state, county, city, pocket, wall, childrens and manuscript maps. The collection can be used to study history, genealogy and family history.
Indeed, it can. The site allows four different ways to view the maps, the easiest of which is the Insight Browser, the coolest of which is the 3d GIS Viewer that "lets you fly through historic maps in three dimensions." The scanned maps are of the highest quality, and may be manipulated and printed.
The collection includes Moses Greenleaf's famous 1829 maps of Maine, showing town and county lines, grants and purchases, and topography. Comparing maps from 1795 through 1860 shows how the counties of Maine evolved. Farther afield, there is an 1857 map of Los Angeles, an 1874 map of Indian Territory (now Oklahoma), and a 1795 plan of the future "City of Washington." Wherever your ancestors lived in the U. S., there will be at least one map in the Rumsey Collection that lends new understanding of their state, county, town or city.