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So, I'm writing a fictional story about gangs and the city I'm using as the setting is loosely based on New York. More specifically, the size of New York City, and the population. I checked on Google and apparently it goes something like this:

*Land area: 783.8 km² *Population: 8.623 million

There are 4 major gangs that rule this city's underworld, each owning/holding an important territory. I am thinking of adding as many minor/small-time gangs as I can and was wondering, how many gangs can fit in a city of that size and somewhat not result in every single citizen being part of a gang, consequently causing total mayhem .

So, how many gangs can fit in such a city?

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    $\begingroup$ I think the question should be "how many gangs can be in the city that won't result in every single citizen belonging to some kind of gang". In The Warriors movie there were 21 gangs. And they were small gangs. The usuall Big Families were omitted. $\endgroup$ – SZCZERZO KŁY Nov 19 '19 at 10:49
  • $\begingroup$ @SZCZERZOKŁY sure. This is what I am trying to ask. $\endgroup$ – Nass King Nov 19 '19 at 10:50
  • $\begingroup$ What do you mean by gangs? Are we talking "make'em an offer they can't refuse" style Mafia bosses, or more street level thugs? $\endgroup$ – hszmv Nov 19 '19 at 13:22
  • $\begingroup$ @hszmv haha 4 of the "Godfather" types, and the rest of the gangs as street level gangs $\endgroup$ – Nass King Nov 19 '19 at 13:24
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It will obviously vary by time period, culture and the effectiveness of law enforcement. For historical perspective, the non-fiction book Gangs of New York describes the gang activity around 1900 up to the prohibition era New York in the 1920s. (The 2002 movie of the same name used this book as source material.) The book lists 42 organized gangs and a number of independents. New York City at this time had approximately 5-6 million people.

The book probably will not be exhaustive, but it gives an order of magnitude estimate of 1 gang per 150 000 people.

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    $\begingroup$ So I thought this was kind of funny, as with 8.623 million it comes out to ~57 gangs which was very close to my number of 54 $\endgroup$ – Hink Nov 19 '19 at 12:24
  • $\begingroup$ @Hink Yeah. It's nice when completely different methods to arrive at the answer agree with each other. Reinforces the confidence in the result! $\endgroup$ – tylisirn Nov 21 '19 at 8:44
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This is impossible to know for sure, but you can do some estimations

So we we are going to treat is like a Fermi problem, and do some broad estimations and hopefully end up in an order of magnitude of the correct answer. Depending on your world, you can change any of these numbers to tweak your answer.

For the ease of math, we will start with a city with 10 Million people over 1,000 Square Km. For the purposes of this problem gangs will operate in cells, with large gangs consisting of multiple cells under a citywide franchise and small gangs being a single cell.

  • 10,000,000 People live in the city
  • 10% of them are in the correct age bracket to join a gang, so 1,000,000 young adults
  • 1% of young adults join a gang, so 10,000 gang members city wide
  • The average cell size of a gang is 20 members leaving 500 cells
  • Assuming a city size of 1,000 km
  • 50% of the city is both valuable and can be controlled (e.g. not landfills or the heavily policed financial district) leaving 500 square km of controllable space
  • Each cell could control 1 km.
  • Going by an 80/20 rule, 80% all cells will be in one of the 4 biggest gangs.
  • Each of the super-gangs has on average 100 cells, 2,000 members, and controls 100 km squared.
  • The remaining gangs are on average 2 cells (the majority are single cell, but there are a few mid-sized gangs), leading to 50 gangs with an average of 40 members controlling 2 square km.

So you have 54 gangs in your city operating in 500 cells.

Also, as the math is listed above, if there are any numbers you think are incorrect for your world, just replace the numbers and re-run the calculations.

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    $\begingroup$ This seems like a low estimate. LAPD currently lists 450 active gangs in a city with similar land area and lower population than NYC. Theoretical max is probably at least a little more than LA currently has. $\endgroup$ – manveti Nov 19 '19 at 19:50
  • $\begingroup$ Yeah, it's due to the 4 super-gangs due to the world and takes up all the members. It would generate around 250 without them, which is still low, but not as far off. $\endgroup$ – Hink Nov 20 '19 at 7:09
  • $\begingroup$ Ah, gotcha. I had misinterpreted that part of the answer. I think the remaining discrepancy can be explained by an underestimation of gang participation rate -- using LA as an example again, roughly 1% of the entire population of the city is in a gang. This is probably due to aggregation across age groups: not all people who join gangs in a younger age group die or leave before graduating to an older age group. $\endgroup$ – manveti Nov 20 '19 at 18:45

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