The once-every-decade process of redrawing legislative and congressional districts is getting under way in state capitals around the country. To start, Sun Belt states will gain and Rust Belt states will lose seats in the U.S. House of Representatives. But win or lose, states have to redraw lines to make sure that legislative and congressional districts have equal populations and give fair opportunities to minority groups. The process is intensely political, with parties maneuvering for advantage and incumbents seeking to hold on to friendly territory. Republicans are in a good position after gaining control of legislatures in a majority of states last November. But demographic trends, especially the growth of Latino populations in some states, may limit the GOP's opportunities. In addition, California and Florida will be operating under new rules pushed by good-government groups that seek to limit “gerrymandering,” line-drawing for purely partisan reasons. After redistricting plans are completed, many will be challenged in court, where outcomes are difficult to predict.