The United States Congressional Serial Set Map Index contains a wide variety of maps on topics as predictable as Armed Forces and Conflicts or Discovery and Exploration to those as unexpected as the Almshouses and Asylums. You can find for example the map titled "Boston in 1880, showing societies (secret and benefit), hospitals, asylums and homes." Maps included date to before 1799. For example if you were studing the Roman Empire you might find interesting a map of the "Main road system of the Roman Empire as shown by the Itinerary of Antonine (A.D. 150) and the Itinerary to Jerusalem (A.D. 333). From Parthey and Pinder."
Anyone wishing to take an online map into the field should consider printing a copy. Commercial providers, such as FexEx Office, offer large format printing services in person and online. University of Delaware users may consider two on campus locations for printing large format materials.
A listing of printed materials available for use in the Library.