How do I decide where to put individual districts/buildings in a big city?

[Best Kog NA]

So I'm mapping out a medieval / fantasy city for a friends D&D 5e campaign, I already figured out the scale, the outline of the city, and where all the major buildings are going, but I'm struggling with where to put everything else in the middle. It's locked between a mountain and a river, so I figure that it must have been a pre planned city, but I can't figure out where to put everything else like housing and businesses. Does anyone here have any tips on how to decide the layout of a city?

[Larb]

If you're going for a preplanned layout then the easiest to go with would be a grid. Your main businesses may likely be along the main thoroughfares. Craftsman who do noisy or smelly work might be tucked away in one corner. Residential housing wherever it will fit.

That's just a fairly generic view - hard to say without knowing more - what the culture is like, is it a walled city, how much space, does the city have a specific function, import/export, and whatnot.

[Azélor]

It's locked between a mountain and a river, so I figure that it must have been a pre planned city

I don't understand what makes you come to that conclusion.
Pre planned cities were not common and still many cities are not planned on the long term
If it is planned, then it is an important city, likely a capital.

Without asking something more specific, my advise would be to look at real world planned cities of that era.
The two I remember right now are Constantinople and Xi'an (Chang'an).

[Pixie]

It's locked between a mountain and a river, so I figure that it must have been a pre planned city

On the contrary, a planned city would be more likely built on a place with space to spare. A city on a tight location indicates that it evolved from an original seed activity without actual long term plan.

Maybe that location had some Riverside hill suitable for a castle for the Lord of the valley, in early feudal settlement times...
and from there a small town emerged, and from there, say, a healthy tannery industry kicked in, pulling in more people...
And then some small iron mines in the vicinity get expanded to supply local demand and a second industry of metal working pulls even more people...
The neighbouring valleys end up being used as farmland, growing economically with feeding this population, making the city even more central with its monthly farmers market...
Eventually a cultural hub, outputting prized swords, quality leather armor, well known for its past noble Lords, whose lineage is long extinct...

Sounds like an European medieval city already.

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[Voolf]

I would guess that it does not matter so much whether the city was preplanned or not. Planned city tends to be more organized with the administration districts, market districts or residential area. The layout are also more man-made looking usually, with 90degrees angle for streets. Azelor mentioned Xi'an which is a good example. Anorther one is Kyouto in Japan, which is also situated between mountains and river.

[Ignis-fatuus]

This discussion of preplanned cities vs more organic cities is is pretty interesting. I think there are a number of ways of going about it. I would rarely do you find cities that are planned right from the git-go; they do exist, however, and can be found in some cities which resulted from colonial expansion--I want to say that the cadastral mapping technique was heavily used in the European settlement of Austrailia.

On the contrary to this, I would argue that more often than not you have a more vernacular used of space wherein houses, shops, and even districts are formed in relation to both the ease of development and strategic placement to environmental features. Later, after the city begins to grow, a more formal pattern emerges as it sprawls outward. I want to say maybe San Francisco might work as a fitting example. Whereas the downtown area is a bit of a mess, by the time you get to some of the outer districts, like the Sunset district, you see a very planned gridded landscape.

In terms of D&D mapping, one piece of advice that I found to be rather interesting is to take a particularly interesting aspect o the city and then expand it to be a defining aspect of the settlement. Not only will it give it a bit of character, it leaves room for some interesting narrative world building.

[randigpanzrall]

Well Best Kog,

at the beginning I would ask myself some questions:

- Is the city of great national or even international importance?
- Is it a large city or a small city, how many inhabitants?
- Is it a large River?
- Is this river shippable and if so, is my city a city with a large port?
- How much space is between the river and the mountains?

Old European medieval cities, even big cities, were only big in the very rare cases and an area of 1000x1000 meters was basically a big and important city.

So I would suggest to answer these questions, keep this facts in mind (without beeing restricted too much by them of cause )

Then I would start with the port, the nearby market place (f.e. 50x50 meters), than adding a church or cathedral, depending on the plannend amount of inhabitants.
After this you can create the mayor streets, crossing the city, adding some secondary streets and adding some residential houses and additional administrative buildings and warehouses and so on.
Even think about a city wall, or some watchtowers or both, maybe a castle or something... Just start and try to grow the city like it would have grown in it´s history