<p><pre><code>    there is probably a point somewhere between 
    those two points where the gains are only 
    marginal.
</code></pre>
I think we have not reached it in any city currently on earth. I think the whole earth&#x27;s population could live in a space the size e.g. of Texas, if that space was as densely populated as London (which is not that dense). In such a scenario it would be near trivial to provide everybody with top-notch public transport, waste disposal and so on.<p><pre><code>   In the latter, you can only walk in your general 
   neighbourhood 
</code></pre>
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.