Congressional district

A congressional district is an electoral constituency which elects a member of a congress. Countries that have congressional districts are Japan, the Philippines, and the United States. The size of a district is based on the number of people who live in that district. A district is often very big if there are few people that live there; a district is often small if it's in a big city because there would are many people living there. 
United States.
The United States has 435 districts. Each district has about 747,000 people living in them.