Who represented the House of Representatives?

Answer 1

Us.

Each representative is elected by the voters in a geographical area called a US Congressional District. Each district is totally within a state, and most states have several districts, one for each representative "seat", each containing roughly the same number of people (of course, the size in square miles may be very different). The number of representatives is decided based on the state's population, so even districts in different states are more or less the same size. State officials redraw the district boundaries every ten years, after the U.S. Census comes out, to keep them of equal size. States may also lose or gain seats based on the census, as their total population count changes.

Generally the party in power will try to draw the boundaries to favor their party. This is called gerrymandering, presumably named after an early practitioner.