Best I can tell is you just grow a hundred different small villages and towns bigger until they overlap and become a single place. And every ten or so years someone else decides how urban planning should be done, so there's no major consistency, plus you've got to work around the shape of the land, the river, the coast, listed buildings, protected views...

London is pretty crazy with those - mostly concerning St. Paul's Cathedral. And buildings are pretty small, and very expensive in the city centre.

Hwo do you get around this? Dig down! Have a new basement or three. And once you've dug it out, you've got a new problem. How to get the digger out again... I mean, your place is too small to set up ramps... and you had to take out one wall to get it in, but to send in a crane would need the upper walls and floors taken out too... and it would mean closing the street... That's really REALLY expensive..

This is why most luxury London houses have a drained, part-stripped and tarp-wrapped JCB buried in concrete under them, like a strange mechanical Pharaoh.


So to summarise how big cities work: You make it up as you go along.