This is one excellent way the city is using old tax records: The city took photographs of every house and building in the five boroughs between 1939 and 1941, and now these photographs are for sale. Go to the NYC Department of Records Tax Photographs page and learn how you can get a picture - you need to know the exact lot number and official block number of the building (of course that information isn't searchable online yet; the DOR says you can use their archives of maps and mentions the word "microfilm"...or you can add $5 if you want the DOR to search for it). This seems like a great gift idea, at $30-45 a pop (not including shipping and handling) for that someone who loves pre WW2 buildings.