Of course there exist many places where we have not reached the point of marginal gains (and hence massive room for improvement), but you don&#x27;t make an argument why you think we haven&#x27;t reached that point anywhere on Earth.<p>I think you underestimate the practical difficulties of providing 7 billion people with top-notch public transport and other public services, and there is no precedent of what a region the size of Texas with an average density of 10k&#x2F;km2 would even look like (though there are artists&#x27; renditions, most of them dystopian). But anyway, if that could be done, it could just as well be done if you split everyone into groups of 200k to 2m and settled them in smaller regions of similar density. And that&#x27;s not a hypothetical, that&#x27;s what we call a city now, and they work fine.<p><i>That&#x27;s true, but why is this a problem? For a sustainable, walkable city it&#x27;s only relevant that all key infrastructure (e.g. schools, shopping, leisure, parks ...) is within walking distance and this infrastructure gets replicated in bigger cities.</i><p>I agree. I&#x27;m not saying that cities larger than 10m are a problem, per se, I&#x27;m just saying that smaller, dense cities get you most of the advantages from a quality of living and services aspect. I think it&#x27;s a matter of taste whether you prefer to live in a city of 50k, 100k, 500k or 2m, and all of these are broadly similar in terms of sustainability.