In 2006, US population reached 300 million people. Estimates suggest that the US population will reach 400 million in about 2039 -- within the lifetimes of many of us. From time to time, I hear concern about where America is going to put 100 million more people.

As Mason Gaffney has pointed out, our current population of about 300 million people, were we to choose an average population density of 10,000 per square mile (that's 16 people per acre, or about 5 to 6 households per acre, on average -- not far off the US median), the current US population could fit into a circular area about **196 miles across**. The rest of the US would be available for other purposes. [The math: 300,000,000 divided by 10,000, divided by 3.14; take the square root to get the radius; double it for the diameter.]

If we wanted 50 cities instead of just one, each would need to be 13.8 miles in radius, across, or 27.6 miles across.

To accommodate the fourth 100 million people we'd need a larger radius for that single metro area: 113 miles -- **a 226 mile diameter circle**. Or, if we wanted 50 cities of similar density, each would be just under 16 miles in radius, 32 miles across.

Since the US consists of 3.5 million square miles, there is a fair amount left for agriculture and other purposes.

Googling "United States" "square miles," I also found at Census Bureau Quick Facts page which provided the following statistic: that we now use 79.6 square miles per person.

- California has 217 persons per square mile (ppsm)
- Los Angeles has 7,877 ppsm
- Illinois has 223 ppsm
- Chicago has 12,751 ppsm
- San Francisco has 16,636 ppsm
- New York State has 402 ppsm;
**NYC has 26,403 ppsm**- Albany County has 563 ppsm

So here's a quick summary: What would the **diameter **of each city need to be to accommodate the US population?

at 300 million population: at 400 million population

one city: 50 cities each: 100 cities each: one city: 50 cities each: 100 cities each:

at 7,877 ppsm: 220 miles 31.2 miles 22.0 miles 254 miles 36.0 miles 25.4 miles

at 12,751 ppsm: 173 miles 24.4 miles 17.4 miles 200 miles 28.0 miles 20.0 miles

at 16,636 ppsm: 152 miles 21.4 miles 15.2 miles 175 miles 24.8 miles 17.5 miles

at 26,403 ppsm: 120 miles 17.0 miles 12.0 miles 139 miles 19.6 miles 13.9 miles

What observations might one make from this?

1. That to accommodate the extra 100 million people, a 33% increase, can be done with either a 33% increase in density, or an increase in the diameter of the city(s).

2. That if population continues to grow, land in our cities will become more valuable.

3. That if population continues to grow, land near our cities will, on average, become more valuable.

4. That we are not land constrained. We could fit 400 million people into a rather small circular area, and have plenty of space left for agriculture and other activity.

5. That those who currently own land in our cities are likely to be wealthier 10 and 20 years from now than they are today, even if others aren't. And with not a finger lifted!

6. Knowing that our population is likely to increase by 33% in the next 30 years, we ought to be shifting to Land Value Taxation as soon as possible, so that instead of enriching a few lucky landholders, we all share in the population-driven increases in the value of our urban and suburban land.

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