[BorgHunter]

What gets more expensive with increasing density? Seems like most things are cheaper with more density, because (compared to less density but equal population) there's less area that needs to be covered by roads, water mains, fire stations, transit service, etc.

[vorpalhex]

..and you'll use 10% more electricity and 10% more water and 10% more fire/rescue calls and so on. You'll need 10% more buses. Your airport will be 10% busier. You will have 10% more people eating at restaurants...

And installing a water main in a rural area is a lot cheaper than installing one in downtown NYC... and your water main needs to be bigger now too.

[BorgHunter]

But I said to keep population equal. Take two million people, and put a million in a city as dense as Manhattan (74,780.7/sq mi), and the other million in a city as dense as Jacksonville, Florida (1,270.73/sq mi). So New Manhattan would be 13 square miles, and New Jacksonville would be 787 square miles. It seems obvious to me that most things in New Manhattan would be more efficient and cheaper. You'd need fewer police officers to have the same patrol density. You'd have a couple larger fire stations instead of numerous smaller ones. You'd have far less utility and road infrastructure to maintain. Everyone would spend less time traveling places, because everything's so close together, and fewer people would feel like they had to purchase a personal vehicle, which means fewer and smaller parking lots to pave. You have to make other tradeoffs for this bonus, of course, and many find those tradeoffs unacceptable, which is fine. But it seems like efficiency is density's greatest strength, to me.

[vorpalhex]

Police officers scale as calls scale. There's some minimum threshold based on space, but if you have 50 calls at once then you need 50-70 officers. And your manhattan officer doesn't have the option of "let the angry dude kick rocks in a farm field until he gets bored and arrest him". Every fleeing perp becomes a danger to _hundreds_ of other people. Every fired pistol round has a high chance of hitting a bystander. CS gas cylinders are right out.

Same for fire, except now you have a new problem. When a house in New Jacksonville burns, one option is to let it control burn. The home is a loss, but this is a safe and viable option.

You can't do that in our manhattan. The entire city will be on fire.

And fighting a fire on a one floor residential house is easy. Fighting a fire on a 40 floor condo structure is complicated and takes many, many more trucks - and now instead of one home being lost, we are looking at ten or more homes, even if we are successful.

Water distribution to a bunch of little houses is easy if sort of requiring some piping. Distributing to a 40 floor condo building is an expert task requiring a whole mess more of complexity.