Things to consider when placing a settlement.

[waldronate]

Start by searching for "central place theory" and it will lead you down more rabbit holes than you ever considered. The basic notion is that goods and services have a radius in which it's profitable to exist. Outside of that radius, another one will appear, leading to (under ideal circumstances of a uniform flat plane populated by perfectly rational producers and consumers) a hierarchy of settlements laid out in hexagonal grid. Real-world constraints such as mountains, rivers, and politics will distort that perfect grid, with sufficient distortion resulting in additional features (e.g. a ferry on a river or a settlement on each side of a mountain pass) or removal of features (that town done got ate by the dragon, that's why). Towns have a tendency to be about a day's round-trip travel away from each other, with various support features at half-intervals. The kind of goods and modes of transport will also play into it and changes in transportation modes will disrupt existing networks (e.g. the advent of the automobile and interstate highway system in the USA badly disrupted many areas in ways still not recovered). There's a lovely article (dissertation?) on why the counties and states are different sizes that you'll come across: read it!

[bognor]

Start by searching for "central place theory"

I really love it when the answer to my question is "Know these three words, in this order, and a new domain of knowledge will open at your feet!"
This was really useful information and you have earned both my respect and my thanks.

A further question - half-asked in my post - concerns tech trees and/or dependencies. Is there a similar magic spell for, tech tree dependencies // food webs ... eg: firearms? Well you need ammo for that, whic requires fine tooling a source of lead (or similar) and black powder, steel for the gun barrels. So black powder - you'll need nitrates, sulphur and ground charcoal for that. Steel? you need high temperatures to remove all the impurities from that iron you smelted .. etc...
I imagine that for each resource in demand, one could model CPT to represent the links and, again, consider value of resource in terms of final availability?