I stumbled across this helpful web site and wanted to share it: Old Maps Online, www.oldmapsonline.org/
It’s a searchable index of old maps available for free online, with links that take you to the maps. Most are available from museum and library web sites, but it’s useful to have them cataloged and searchable in one place. The majority of the maps are from the nineteenth century, but some are older or newer. They range from world maps to detailed maps of cities. Just playing around on the site, I looked at Civil-War era maps of the military defenses of Charleston, South Carolina; maps of the West Indies during the height of the sugar plantation era; street maps of cities my ancestors lived in; and a detailed map of colonial-era Calcutta.
This is a great resource for writers of historical fiction, family historians, historians of a particular locations, and anyone who likes old maps.