Some new tools are online that let you see how an area used to look.
The USGS has made available 125 years of Historical Topographic Maps
So much wilderness east of town in the 1950's
Another site is WhatWasThere.com
This site lets you overlay historical photographs over Google Street view.
Park Place Hotel.
Found some other sites that show how cities have traded density for parking lots. So I took their photographs and made animated gif's out of them (sorry, at least the animated gifs aren't from an old geocities site).
The Atlantic on how parking lots ruined Cleveland's warehouse district: Cleveland's Disappearing Warehouse District, Then and Now
Thoughts on the Urban Environment has a similar example from St. Paul: The last 47 years have not been kind to 7 Corners
These images remind me of an online tool from MIT Media Lab called Place Pulse.
What they do is present two similar images from cities and present the question "Which place looks safer, more unique, or more middle class?" You're asked to click on your choice as quickly as possible. This gets repeated hundreds of thousands of times with people from all over the world and the results are grouped into what humanity as a whole regards as safe, unique, or middle class.
You can view the results without going through the process.
What is clear is the human brain perceives urban density as safer than parking lots.