David Rumsey Historical Map Collection is often the first place I go to when looking for old maps to use in a social studies lesson. The collection contains more than 100,000 historical maps documenting places throughout the world. The maps can be searched by area, by time period, or by cartographer. There is also a Google Earth layer based on the maps in the David Rusmey Map Collection.
Old Maps Online is designed to help you find historical maps of where you live or any other location that you enter into the search function. By default Old Maps Online searches for maps near your location. You can refine your search to a specific time using the timeline slider on Old Maps Online. Old Maps Online doesn't host the maps that you find through their search box. Old Maps Online refers you to the host of the maps. The David Rumsey Historical Map collection is one of the sites that is indexed by Old Maps Online. Old Maps Online also indexes collections from the British Library, Dutch National Archives, Biblioteca Nacional de Colombia, Harvard Library, and collections from nearly a dozen other libraries around the world.
Historic Map Works is an online gallery of hundreds of historical maps. On Historic Map Works you can browse for maps by continent, country, state, and province. Contrary to my initial experience, downloading the map images is not free. But, you can view more than half of the maps as Google Maps overlays using Historic Map Works's free Historic Earth Basic.
Applications for Education
One of the ways that I've used historical maps in my classroom in the past is to have students evaluate the role of physical geography in the outcome of significant battles in the American Revolution and the American Civil War. I've also had students use historical maps to compare our current understanding of the world with that of cartographers of the 15th and 16th centuries.
Glenn Wiebe recently shared a set of Smithsonian interactive activities in which students compare the views of modern cities with those of the 19th century. Glenn's post inspired me to look back at the historical map collections I've used in the past.