Brooklyn, N.Y.

2008 Population: 2,300

2012 Projected Population: 20,000

Notable Investment: $950 million for the proposed Barclays Center sports arena

Brooklyn's downtown has emerged as a cultural center with the planned Brooklyn Academy of Music Cultural District project converging underutilized areas into new housing and art space.

Challenges: In addition to resistance from community groups seeking to block the development, the slowing economy has forced many of the original plans to be scaled back or canceled altogether, most notably the stalled Atlantic Yards project and the canceled 100-story, Renzo Piano-designed City Tech Tower.

Source: Downtown Brooklyn Partnership