Looking at the pictures in the article, the level of detail is not particularly great in some parts. It seems like many building have very simple shape and color. With some modeling skill, I can imagine carving and painting 100s of these in a day. Although I can't imagine doing it for 20 years.

I would however like to know what his research was like. Was he just following Google Maps/Earth? They were released in 2005 and 2001 respectively and NY has had coverage from the get go.