&gt; But it would be really interesting to have cities with that have 200k - 1m inhabitants and are extremely dense like central Hong Kong. They may be big and dense enough to have the economies of scale of their larger rivals. But, as pointed out by &quot;vidarh&quot;, they would not remotely match megacities in terms of interesting cultural life.<p>I think with that kind of density, if you go to 1m-2m size, you have a sufficient base for very regular high capacity public transport to other similar sized high density cities very near.<p>E.g. Macau fascinates me (though I&#x27;ve never visited). It&#x27;s a fairly small city - roughly 	643,100 people (2015 estimate)  - , yet it&#x27;s spread out over a positively tiny area - about 30km^2. Overall density of 18,568&#x2F;km2. If you condensed London into smaller cities with that density, you could have e.g. split London into four cities of about 120km^2 each, and still free up more than 1000km^2 for green belts or low density zones around them, and yet they&#x27;d still be near enough to each other for it be pretty much as easy to travel between the areas as today, and the increased density in each city might even cut down total travel times in many cases.<p>The biggest challenge with something like that would be disciplined planning, beause obviously if you put big, dense cities like that near each other, the land in between would become immensely desirable.