The big list of links a couple posts back, are related to housing costs, not housing density. The two could line up if based purely on market demand, but often do not, due to zoning, large swaths of low-density suburban areas built in past generations and whose residents want to keep it that way, desires to preserve the character of a neighborhood for aesthetic or historical reasons (such as the huge swath of single story houses between San Francisco's peaks all the way down to the ocean to the west), not blocking the sights (as my French teacher said with regard to building height limits around the Eiffel Tower), and a host of other reasons. In many of the above, a small ranch (single story) house on a small lot will cost you a million dollars, and the density is low.