After locating a building, click "Show Additional Information" and data will be provided such as lot frontage, depth and area; year built; gross floor area; number of residential units; and whether it has been designated as a Landmark building.
If you click on the camera icon you get a slider with years on it, and get aerial photos taken in those years.
To access the maps and aerial photographs, go to: http://gis.nyc.gov/doitt/nycitymap
My thanks to Harold Miller for telling me about this free web site.
