Harvard housing economics expert Edward L. Glaeser parses the latest Census bureau data for a clear explanation of why high-volume home building will stay concentrated where it is for the foreseeable future. Local land constraints. Glaeser, in a New York Times analysis, puts an economic and climatic test to the fastest growing states, and comes up with this explanation: "A rich body of research shows that regulation, which is intense in the Northeast and California but lax in the Sunbelt, explains why housing is supplied so readily down South. The future shape of America is being driven not by quality of life or economic success but by the obscure rules regulating local land use." Makes Census.