By Chris Adams

In 2020, a presidential election is expected to captivate the nation.

But for the number-crunchers in the U.S. Census Bureau, and the map-makers in statehouses around the country, the real battle will take place far away from the ballot boxes.

After the 2020 census is completed, federal officials will reapportion the U.S. House of Representatives based on population, taking seats from a handful of states and adding them to others. After that is done, it is time for redistricting, a process by which state lawmakers, elections officials or independent commissions build congressional district maps.

In a session with National Press Foundation Paul Miller fellows, redistricting expert Michael Li of the Brennan Center for Justice at the New York University School of Law gave an overview of that process, as well as the concept of “gerrymandering.” With gerrymandering – named after a 1800s governor of Massachusetts – district lines are drawn in such a way as to boost the chances of one party over the other (or one racial group or another).

Li (bio, Twitter) led fellows though a description of the challenges the U.S. Census Bureau will face in 2020, given its budget constraints. Right now, projections show that six states could gain House members and nine could lose them.

Li also described the basic requirements for redistricting, such as what it means that districts are supposed to be contiguous or compact, what it means to keep communities of interest intact, and what the rules are for handling city or county boundaries.

“The one thing you will find about redistricting is that the rules are very vague, and sometimes they conflict,” Li said.

Gerrymandering has been a feature of U.S. electoral politics from the earliest days of the nation’s history. It’s not only for partisan gain; it also has been used to give minority voters more of a say in elections by grouping African-American or Latino voters into a single district, rather than spreading them into several districts and thus diluting their voices.