POPULATION SLOWDOWN: Nearly half the National Football League's teams are in communities with populations that are growing slower than the national average.

CITY RIVALRY: A few decades from now, several fast-growing communities will be able to boast potential fan bases that will far outnumber those of some current teams.

LARGE CONTRAST: Pittsburgh, whose Steelers play the Seattle Seahawks in this year's Super Bowl game, has lost more population than any other metropolitan area in the country since 1990. Seattle, on the other hand, is one of the nation's fastest growing markets.