The OldMapsOnline Portal is an easy-to-use gateway to historical maps in libraries around the world.
It allows the user to search for online digital historical maps across numerous different collections via a geographical search. Search by typing a place-name or by clicking in the map window, and narrow by date. The search results provide a direct link to the map image on the website of the host institution.
" . . . online digital map collections searchable and accessible through the OldMapsOnline portal. Nearly all the institutions providing online map collections have a much larger paper map collection available at their respective institutions, but the OldMapsOnline portal will only search and provide direct linkage to the online maps."