Historic Earth is a mapping app that permits you to overlay historic maps on modern maps, which can make for fascinating study and underscores one of the ways the iPhone can be a great research tool and school aid. It claims one of the largest collections of geo-coded maps of any app anywhere.

Historic Earth allows you to detail your current location, view locations features or search for a specific location as well, making it flexible and easy to use, and you can compare the two maps, both current and historical from any date from the 1700’s to the late 1900’s. You have full pan, scroll and zoom capabilities.

Currently, the 32,000 map database includes maps for the Midwest, Washington State, Florida, California, Alabama, New York, Maine and Washinton DC. Maps are added all the time, so eventually it’ll have all of the US in there.

This one is $5.99 in the App Store, and is worth a look if you’re a geography buff.