Baltimore is the 30th-largest US city by population and is a study in contrasts. It has a low average income compared with other wealthy Northeast cities, has nine colleges and universities, and is a magnet for people pursuing higher education but has undergone decades of population loss. A large social sector provides important services to residents and buoys the local economy: nearly every third job in the city is with a nonprofit employer. But this also illustrates the city's limited economic vibrancy. This mix of market and nonmarket forces makes Baltimore an important place to examine the geography of opportunity in an American city.