Quote Originally Posted by Gumboot View Post
My first bit of advice would be to decide right at the outset how far down the realism rabbit hole you want to go. If your fantasy world is nothing more than a pretty backdrop to your story, the details really don't matter, realism (within reason) doesn't matter, and you should just go with what you want to go with.

At the opposite end of the spectrum you can meticulously create a fully realised world in intricate detail.

I personally tend towards the more realistic side of things, so I've put pretty extensive work into these sorts of things. I'd never do it any other way, but it's worth pointing out that going down that route means a LOT of extra work. And I put "lot" in capitals for a reason. Seriously, you cannot underestimate how much work it is.

To answer your specific questions above though:

The first thing is to understand the structure of feudal medieval living, and the different classes of habitation, because they're quite distinctly different. Towns and cities are not the same thing, at all.

The first thing is that both towns and cities are significantly smaller than what you or I think of as towns or cities, and the second thing is that villages are much larger than you or I think of them.

Medieval society existed in dense networks of villages, about 2-3 miles apart, in every direction. The villages only stopped when they encountered land that couldn't be cultivates. Villages were quite large, typically around 700-1,000 people.

Towns appeared at random, in the midst of these dense village networks. The primary purpose of the town was to serve the immediate area; it was a central trading centre for the villagers to buy produce that they couldn't make themselves, and to sell excess grain/wool/fruit/whatever their village produced. As such, towns were quite small, and there were a lot of them. A typical medieval town will only be between 1,000 and 8,000 people.

Cities are a different beast all together. While towns serve regional trade, and emerge based on local requirements, cities serve inter-regional trade, and emerge based on the routes that feed goods into the towns. Typical sites for cities include points where routes to multiple towns meet, and ports and harbours that bring in goods from overseas.
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Also don't forget that some towns spring up where travelers rest or at crossroads a small inn in between two major cities on a trade route could eventually turn into a town