New York changes all the time--buildings go up, bars close--but one thing, I hope, will always stay the same: the city's obsession with self-documentation. Maybe it comes from how transient the landscape sometimes seems, but government and citizens alike absolutely love mapping the city's history.
Last year's quadricentennial brought us Manahatta, Eric Sanderson's revolutionary study of Manhattan's natural landscape before and after Dutch settlers arrived. The book is great; the corresponding interactive map is way cooler.
We also got a great exhibit at the Public Library, Mapping New York's Shoreline, packed with 400 years of cartography that shows the city grow up around its rivers. (It's still up, if you're curious.)
A look back to the recent past sent The New York Times photographer in November to a dozen buildings around the city to follow up on a 70-year-old project that documented 700,000 properties in "tax photos." (You can buy photos of your apartment from either the first project in the '40s, or the second in the '80s, here.)
And now, the city government's on-line map has added hi-res aerial photos from 1924--it's awesome. Check out Dodgers stadium, or the Brooklyn Navy Yard. Watch the Verrazano Bridge appear, and Penn Station get leveled. Or just put on some Bessie Smith, mix a Manhattan, and fly around the bygone city.