The rules for the redistricting process are left up to each individual state. In California, we have an independent commission called the California Citizens Redistricting Commission (CCRC). I remember there was a portal online where you could write in to the commission describing what you considered your “local community.” They then took the input from individual citizens and advocacy groups and drew up new congressional districts based on it, while making sure they were roughly equal in population, and that they weren’t drawn in a way that would purposely dull the voting ability of a particular group.