New York City, home to a disproportionately large number of people living in buildings constructed decades ago, is especially rich in reminders of those who occupied our houses and apartments long before we did. According to the 2008 Census housing survey, 85 percent of New Yorkers live in buildings erected before 1970, compared with 42 percent of Americans generally. More remarkably, 39 percent of New Yorkers live in buildings predating 1930 and 17 percent in buildings predating 1920. Luckily for New Yorkers with a taste for past lives, many of these dwellings function as palimpsests of the city’s history.
http://www.nytimes.com/2011/04/10/realestate/10cov.html?_r=1&pagewanted=all