Principal Real Estate Investors will pay the city of San Francisco $15.1 million rather than include below-market-rate apartments in a 52-story residential tower it is developing at the top of the city’s Rincon Hill. The project is part of the rehabilitation of the area, once one of San Francisco’s most exclusive neighborhoods. According to Insurancenewsnet.com, this is the second phase a project in which Principal Real Estate Investors is a partner. California cities provide a range of alternatives to providing below-market-rate units, including deposits into housing funds or construction or rehabilitation of units at another location.