Housings costs are an issue in Chicago, and aldermen are worried that as gentrification sweeps through neighborhoods, long-time residents will struggle to pay rising rents or be forced to move. There are ways to help lower-income Chicagoans stay in the city, including affordable housing programs that require investors to include less-expensive units in or near new developments. These investors can be compelled by city officials to increase their generosity. On Tuesday for example, Sterling Bay said it would include 600 affordable housing units — twice as many as required — in its massive Lincoln Yards project in hopes of winning city approval.