Have some time to kill before checking into your next (defunct) favorite old bar on PastMapper? David Rumsey Map Collection features 120 of the world's coolest old maps from 1680 to 1930 and overlays them on Google Earth — adding functionality that goes way beyond a simple image scan. You can go back to a time when, Manhattan was filled with stables and asylums, not condos and Shake Shacks.
Or visit San Francisco, circa 1915, when Fisherman's Wharf wasn't such a nightmare. And check out the nice detail you get when zooming.
The size of the cities in these maps is astonishingly small, compared to the current urban sprawl. Here are Beijing's city limits in 1930.
Anyways, given that Rumsey's entire collection numbers around 150,000, be happy that there are only 120 online now. (Thanks to Eric Slatkin for posting on Facebook.)