Start with the Coastal Megalopolises: New York, Los Angeles, San Francisco, San Diego, Chicago (on the coast of Lake Michigan), Miami, Washington and Boston. Here is a pattern you don't find in other big cities: Americans moving out and immigrants moving in, in very large numbers, with low overall population growth. Los Angeles, defined by the Census Bureau as Los Angeles and Orange Counties, had a domestic outflow of 6% of 2000 population in six years--balanced by an immigrant inflow of 6%. The numbers are the same for these eight metro areas as a whole...
The result is that these Coastal Megalopolises are increasingly a two-tiered society, with large affluent populations happily contemplating (at least until recently) their rapidly rising housing values, and a large, mostly immigrant working class working at low wages and struggling to move up the economic ladder. The economic divide in New York and Los Angeles is starting to look like the economic divide in Mexico City and São Paulo.
The Kling Scenario is where immigrants displace native-borns on the poverty rolls. In an email, Kevin Lang put a damper on that thesis, saying that poverty among native-borns remains high, at 12.1 percent, compared with 12.6 percent overall.
However, there are potential "new entrants" to poverty other than immigrants. Divorces create new poor families. Also, young families tend to start out poor relative to their eventual incomes.