Why 1950?

Why are today's Census figures being compared with those from the 1950 census?

1) Because 1950 was when most of the big industrial cities of the Northeast and Midwest (Baltimore, Pittsburgh, Detroit, St. Louis, etc.) reached their peak population. After 1950, the population of these cities went into a steep decline as jobs and people moved to the suburbs and to the distant cities of the South and West.

2) Because after 1950, thanks in part to the development of air-conditioning, the cities of the South and West (Charlotte, Dallas, Phoenix, etc.) started to grow like crazy as people moved there for warm weather and jobs.