Which district has the largest population?
select district_name from district order by city_population desc limit 1
What is its headquartered city?
select headquartered_city from district order by city_population desc limit 1
What is that city's area?
select city_area from district order by city_population desc limit 1
How many cities have a population over 500,000?
select count ( * ) from district where city_population > 500000
What are the names of those cities?
select headquartered_city from district where city_population > 500000