The Northeast Corridor and Interstate 95 link an almost contiguous sprawl of suburbs and large and small cities, forming the Mid-Atlantic portion of the Northeast megalopolis, one of the world's most important concentrations of finance, media, communications, education, medicine and technology. The Mid-Atlantic is a relatively affluent region of the nation, having 43 of the 100 highest-income counties in the nation based on median household income and 33 of the top 100 based on per capita income. Most of the Mid-Atlantic states rank among the 15 highest-income states in the nation by median household income and per capita income. The region is home to some of the most prestigious universities in the nation and world including Columbia University, Cornell University, Johns Hopkins University, the University of Pennsylvania and Princeton University, which rank among the top 20 universities in the United States and the top 25 universities in the world.