You're worldbuilding here, even if it isn't a whole world. That's a huge task if it's done properly, but most of us manage with a very basic understanding of how things work on a very general level.

Manmade terrain, like farmland, will tend to be at the lower altitudes where there is fertile soil and water, so the river idea isn't as bad as you think. but perhaps it would be easier to place the farmland if you add the settlements and roads, since no one is going to farm a fertile valley that is hundreds of miles from the nearest large town, and which has no roads to transport the food to that town.

Settlements themselves will tend to be on the coast where there is good fishing or good access to oceanic trading routes, preferably both. Or they will encroach inland up the larger rivers, particularly if there are resources to be had - like timber, mineral ores or just to farm the land to feed a growing city at the mouth of the river. They can also arise along major overland trade routes, particularly where these cross natural barriers like rivers or either side of a mountain pass.

Wherever man isn't building cities or farming, the rest of the land will probably be far more dependent on climate and altitude. After all - why waste magic on land that is no use to man?

Forests have tree lines that respect both altitude and latitude. Deserts, with a few really obvious exceptions, tend to appear at 30 degree latitudes on Earth because of the lack of rainfall where the Hadley Cell circulation causes descending air. https://en.wikipedia.org/wiki/Hadley_cell Deserts also appear in places like Chile over a much wider range of latitudes, where a cold sea current flows up the South American coast from Antarctica and fails to fill the air with moisture, causing little or no rain to fall on that side of the Andes.

That's more than enough to be thinking about, so now on to the practicalities of making that swamp and marsh terrain work together.

Both of those terrains are placed on the same sheet by their respective drawing tools, called LAND FEATURES. So where they overlap the Edge Fade, Inner doesn't fade the edge of the individual polygons, but only the outside edge of both the polygons taken as one mass

The solution is to add a new sheet either just above or just below LAND FEATURES and call it something suitable, like LAND FEATURES 2, copy the sheet effects from LAND FEATURES to the new sheet, ok that and then move either the marsh or the swamp texture to the new sheet.

Here I have moved the swamp fill to the new LAND FEATURES 2 sheet, which places it above the marsh and fades the edge.

If I want them the other way around I might move LAND FEATURES 2 above LAND FEATURES in the sheet list, or move the polygons, each to the other sheet.

You can draw your own quite easily in any bitmap app. GIMP and Krita are free. I use Affinity Photo and Designer myself, rather than paying rental for PS.

Importing them and making your own symbol catalogues is really easy. Remy has done a series of videos covering this here:

https://www.youtube.com/playlist?list=PLulP-cGMLxw4qTpXfilRHgbDUg8WvrEX2

Possibility 1: EDIT: read further down the tread - this is actually wrong, but I will leave it here to maintain the record of why people said what they said.

Varicolour symbols only work if you open the catalogue, not the folder.

Click the open folder button at the top of the symbol list and open the [catalogue file name].FSC file, rather than the folder.

You might need to purge the existing Flower Shrub symbols from your drawing, save it and reopen it first, or CC3 will remember the first definition for that name and continue to paste the old symbols instead of the new working ones by the same name.

...

Possibility 2:

You have an old installer back from when the set was first published. I think it was corrected some time ago, so a fresh download and reinstall might put it right.

That's a good idea, Quenten.

@jmabbott I would put a modified selection in front of them made up of all the ones you think would be more suitable, and explain the problem with using a more detailed style printed so tiny.

You may need a style that is more simple and straightforward with simple blocked in houses and no fancy artistic stuff going on. A highly detailed style like Darklands has a tendency to look quite horrible when printed so tiny. There wouldn't be a problem if this was intended as a poster map to put on the wall, where you might still expect to pick out the details of individual rooftops and chimneys, but it isn't.

If you have a free hand to suggest other styles I recommend something like the Ferraris Style, which is more suitable for larger areas printed small, or the more recent Tactical Maps published in April this year in the Cartographer's Annual. Something more Ordnance Survey in style than artistic. There are other relatively simple styles to chose from, of course. Have a look at what you've got and take the time to consider carefully just how much detail you really want when each house will be little more than a squashed ant in size on the finished letter-sized map.