This article was a successful audition for a job writing for an agency. They liked the comparison I set up in the introduction.

In the contest for the largest of something, the answer is sometimes simple:  the largest planet in the solar system is Jupiter, which has an equator that measures almost 143,000 km (nearly 90,000 miles).  It is also the heaviest planet.  Sometimes, however, the answer is not clear-cut.  For example, what is the most heavily populated city in the world?

The most populated city in the world is Tokyo, with a population of 38 million people.  However, this includes the metropolitan area.  If you only count the people in the area under the direct jurisdiction of a city, then Chongqing, China, wins the prize.

How is this possible?

What is a City?

To define a city, we first need to agree on what we call a city.  The United Nations classifies cities in three ways:

• Municipality.  The municipality is the area of an urban area that is under the direct control of the government of the city.
• Metropolitan Area.  A metropolitan area encompasses the area around the city that is also densely populated.  Areas outside of the municipality are still linked to the city via commerce, labor, and transportation. 
• Urban Area.  An urban area is similar to the metropolitan area with one difference.  Rural areas can be considered part of the metro area if they are economically linked to it.  However, they cannot be considered part of an urban area.

If measured by metropolitan area, Tokyo, with its 38 million people, is the most populous city.  However, if you’re counting municipalities, it falls to 11^th place, behind cities like Beijing, Delhi, and Istanbul.  Tokyo rises back to first place, though, if you count by urban area.

A Municipality Can Define Itself

When measuring population by a municipality, five out of the top six cities are in China.  This is due to the size of the cities.   For example, Chongqing contains 82,000 square kilometers within its border while Tokyo has just under 2,200 square kilometers.

Population Density

Everyone agrees (except maybe the flat-earth people) that a mile is a mile.  When measuring the number of people who live in a square mile, it’s an apple to apple comparison.

If measuring by density, then Tokyo falls to 50^th.  Mumbai, India, has the highest population density, with almost 77,000 people in one square mile.  Madrid is the 42^nd most densely populated city, London comes in at number 43, and Barcelona at 48^th.  No city in the United States is in the top 50 most densely populated cities.

Bottom Line

Sometimes the biggest is the biggest, and sometimes the biggest depends on how something is being measured.  Whether the answer is Tokyo, Chongqing, or Mumbai, we can all agree that’s a lot of traffic jams.