WHY DO THE POOR CHOOSE TO LIVE IN CITIES?

In the recent edition of Yale Economic Review (link), Ed Glaeser, Matthew Kahn and Jordan Rappaport ponder one of the most difficult and challenging puzzles of urban economics:

"The 2000 U.S. Census shows that the average poverty rate in American cities drops significantly, from about 20% to 7.5%, as you move from the CBD of a city to its suburbs. How can we tell that this connection between city residence and poverty comes from treatment – that is, cities make people poor – rather than from selection, where the poor disproportionately move to central cities? Here, the data support selection: although ghettos may exacerbate poverty, poor people move disproportionately to the center of the cit- ies, either when switching homes or moving to a new metropolitan area... Given the high proportion of the urban poor who are Black, one might think that inner-city poverty is really just another example of the segregation of minorities. However, [the authors] found that poor Whites have roughly the same central city - suburb poverty gap as Blacks, so it is unlikely that race plays an important role in the centralization of the poor."