Age of Wonders 4 has a random map generator, but normally you cannot tweak that one much. You can select a "geography trait" like Islands, Continents, or Land, and you can select a few other traits. But you can't for example select how many continents you get on a Continents map, or how many mountains on a Land map. Now the Land maps in AoW4 didn't really work for me, as they had far too many mountains. Basically they were designed as a few areas big enough for a city, separated on all sides by mountain ranges, with only a few narrow valleys connecting them. The AI was seriously hampered by that, as crossing a mountain range with a big invasion army needs more coordination than the AI can muster. So the AI was very much funneled by the valleys into very predictable pathways, while the player had the means to seriously abuse this, up to flattening the mountains with the Earth Shatter spell. Also, you could choose the Industrious culture on the Land map, which has scouts that can get rewards from visiting mountain provinces, and that was seriously overpowered on a map with that many mountains.

So my mod reduces the number of mountains, and thus opens up the map considerably. Players and AI have a lot more options to go in various directions. Furthermore, as it turned out, the default Land geography was created by turning lakes into mountains, so there was absolutely no water on the original Land maps. I turned that off, and so now there are a few lakes around, which can be interesting for a city to have as requirement for some buildings. Lakes are also easier to cross than mountains.

While Paradox provides modding tools for Age of Wonders 4, they are far from easy to use, and the available guides from Paradox aren't great. And some things inexplicably simply don't work; for example I first tried to select a different option for the "turn lakes into mountains" function, turning the lakes into grassland. But that resulted in a mod that would always just crash the random map generator, although the option "grasslands" was selectable in a list. Most of the time the problem with creating a mod is that it is very hard to find where a specific game behavior is programmed inside the many available .rpk files. For example I would have liked a mod that changes the starting Imperium to be something other than zero, but I can't find where that is defined. I can find the multiplier for easy/normal/hard, and the income of the throne city, but not the numerical starting value.

Once I had made my mod, it wasn't obvious how to upload it. The guide from Paradox said to use the "publish" function in the Package Manager, which is the central modding software. Unfortunately that information isn't correct, and there is no such "publish" function in that software. Instead one has to make a mod for oneself, and then go to "all installed mods" in the AoW4 launcher, where there is an option to upload the mod to either Steam Workshop or the Paradox website. What it doesn't tell you anywhere is that for the Steam Workshop you also need to make a copy of the thumbnail.png file, which is in the meta_data subdirectory to the main directory of the mod, otherwise Steam Workshop isn't showing a thumbnail icon.

While I made a few other mods for myself, I don't consider them universally interesting enough to upload. There aren't that many people making AoW4 mods, and many of the mods in the Steam workshop have been rendered non-functional by the two major patches that came with the DLCs. But I now know how to write a mod that tweaks the parameters of the random map generator, and could now build maps that couldn't be made without a mod.