Honours Blog #9 – EU4 Map Modding Basics

Map Modding Basics

As in all strategy games, the map is the very core of the game. This goes the same for Europa Universalis IV and this mod!

As the next few posts relating to the mod development will be map-centric I thought it’d be a good idea to familiarize any readers with making an EU4 map works and what kind of files and maps you actually need.

The EU4 Map

The core map files

To make the map above you will need at the very minimum a:

  • -Heightmap and Normal Map
  • -Terrain Map
  • -Rivers Map
  • -Trees Map
  • -Color Map
  • -Province Map

The first steps I took to making the Mod was to create my own version of the above.

So what do these even mean? Well keep reading and i’ll tell you!


Height Map and Normal Map

(Left) Heightmap, (Right) Normal Map

If you’re familiar with 3D modeling then this is pretty much what you’d expect:

The grayscale Heightmap handles the elevation of the terrain in the 3D in-game map, with whiter shades being higher elevation and darker being lower.

The Normal Map (also known as a bump map) is generated from the Heightmap and accentuates differences in elevation by creating a fake lighting shadow effect

In terms of EU4 and other Paradox games if you have a plain heightmap with the basic gray for land and darker gray for water and no other elevation, you’ll end up with a flat map – which is perfectly fine if you’re looking for the absolute minimum in creating a total conversion mod.

Also, heightmaps need to be in grayscale mode but if you just convert it normally in Photoshop (Image -> Mode -> Grayscale) i’ve found that it makes the image fuzzy and not pixel-perfect. An alternate I found is to do it via Indexing (Image -> Mode -> Indexed Color -> Grayscale).

Terrain Map

EU4’s Terrain Map


The Terrain Map affects the game both mechanically and visually:

  • -Mechanically, it determines which terrain type each province is (for example a province in the desert will have the ‘desert’ terrain in-game which will effect how prosperous the province is or how many soldiers can fight on it at once or how quick armies can move across it)
  • -Visually, whatever terrain type you put on this map also shows up in-game – if you place the desert terrain on the map, then it’ll look like a desert in-game

Like other maps used in EU4 the Terrain Map uses Indexing, in which the file is restricted to a specific RGB colour palette which translates to something in-game, if you don’t index your map properly (or use the wrong index) then any attempts in loading the game will crash. Remembering to index your files is an early lesson any modder using Paradox’s Clausewitz Engine will learn.

An example of the colour index in the Terrain Map is Desert (206 169 99), Plains (86 124 27) and Hills (0 86 6).

You could potentially add more terrains by editing the terrain.txt but I given my setting is set in a world where geology and earth sciences are pretty much the same, I don’t really need to!


Rivers Map

EU4’s Rivers Map

Much like the Terrain Map before, the Rivers Map also has its own colour Index and also informs the engine both mechanically and visually:

  • -Mechanically any province that has a river flowing through it will get a River Crossing Penalty modifier, which effects rolls in combat (covered in Honours Blog #8)
  • -Visually: there’s rivers of the map!

As for the colour index there are several types of blue which indicate the size and width of the river, the darker the blue the stronger and wider the river. There are also other colours such as Red, Green and Yellow which handle where the rivers join together, where rivers start, and where rivers diverge in deltas, respectively.

Another thing of note is that all rivers must be 1-Pixel-Thick, so if you have a bit of your river thats accidentally got 2-pixels then it wont show up! Paradox map modding is all about being pixel-perfect!


Worldbuilding Rivers 101

In terms of worldbuilding, one thing learned from /r/worldbuilding is rivers actually work:

  • -Rivers don’t diverge, they converge – meaning Rivers dont split, they join!
  • -Rivers flow from the highlands to the lowlands and always follow the path of least resistance – the end of rivers will always be one exit (Delta’s like the Nile is an exception!)
  • -Rivers don’t link two oceans together, aka you cant have a river that goes from the the north of France at the English Channel all the day to the south of France and link to the Mediterranean – this is because its not really a river anymore, you just made a really narrow ocean and split France into two islands!
  • -Rivers are like trees, at the mouth of it you have a large trunk which leads to the ocean and as you go up you go to branches then to twigs

This might be simple enough when you read it, but a lot of novice worldbuilders who don’t look into these kind of things make this mistake all the time!


Trees Map

EU4’s Trees Map









Same thing as last time, the Trees Map has indexes which indicate the types of trees we have: in general the green trees are temperate forests and the blueish-green are the coniferous huge pine trees we see in places like Canada and Russia.

For some reason the Trees Map is of a different size and resolution than the other maps which causes a bit of an issue in making trees appear exactly where you want them, eventually I realised that I could simply resize my own trees map to the size used here and work on it from there.


Design change relating to trees and terrain placement

Players were often confused whether a province had this terrain or that terrain, or if they were forested or not so Paradox has recently changed their design ethos surrounding both trees as well as terrain:

  • -Instead of trees and terrain overlapping into several provinces like real life, trees and terrain will be influenced by the actual province shape itself.
  • -This means that Marshland provinces will clearly have majority or the entirety of its shape filled with Marshland terrain, and this also goes to Forest province – which will be entirely covered in trees.

While this does go against the believably and realism, it does help the player discern better what they are getting into with a glance instead of having to properly click the province and examine its terrain type

This of course will influence my worldbuilding and development of the map (aha! a link to the dissertation!)

  • -Essentially, the bounds of forests and terrain will be influenced by the shape of the province I make or vice versa, depending on where I had previously said “This place will have a forest, or this place will have a marsh” the shape of the provinces I draw will have to conform mostly to that idea


Color Map

EU4’s Spring Color Map, there’s one for each season! (note America is missing as EU4 has a Random New World option where you get a unique America instead of the one we all know and love)

The Color Map is purely aesthetic and adds the detail you want in your map. The Terrain Map alone only does the minimal and just tiles the same terrain type over and over again so the Color Map helps hide that and makes this look more natural.

I’m still not sure how I’ll do this yet (as my map is made-up, after all!) but this will be something I tackle later on as it’s not really needed to get the mod up-and-running.


Province Map

EU4’s Provinces Map

The bread-and-butter of all Paradox strategy games.

The Province Map does not conform to Index colours like the ones before but it does care greatly about RGB values:

  • -Each province has a unique RGB that is used to refer to it
  • -This links to the definitions file which has every single province in their game, their Province ID and what RGB value that ID is associated with

You can always add new provinces in the definitions by simply editing it, adding a new ID and a new RGB colour (which this handy tool helps you with)


Provinces and Map Overhauls

In terms of development I was conflicted on how to handle this, I had to make my own province map but I didn’t know how to go about it: I was either going to:

  • -Create my own custom definitions file and make up RGB colours as I go
  • -or just use the same colours as the existing one, and just edit the province.txt files later

In the end I decided to go with the latter, as it allowed me to fill out provinces faster as I just had to colour pick, paint and go to the next colour

This would mean that when I start up my mod and have the existing province RGB’s used, the provinces will correlate to the EU4 provinces (eg i’ll have a Paris province in my mod). This can be fixed by editing its specific province.txt file (which we’ll cover in the next next EU4 Mod post)

How I organize my province painting

Thanks to a handly little Province ID map I was guided to (here), I overlayed that ontop of the basic province map so I know which colours go with which ID:

  • Black areas are province i’ve already used in my own Province Map
  • The process goes like this:
    • -Find the next ID along and what color it is
    • -Use Color Picker tool to get the color
    • -Fill in the used province with Black
    • -Go to my Province Map and draw a new province
    • -Rinse and Repeat

A problem I’ll face later on is not knowing what ID my provinces are when I go about changing their names and statistics, but I can just bring back the default Province Map (without any black filled in areas) and try to compare colors and IDs from there or more likely I can get rid of the province name localisation files which will turn each province’s name in game to something like this: PROV1, PROV2, PROV300, etc




EU4 Provinces Colorpicker (2017) Georgi.hdinteractive.com. Available at: http://georgi.hdinteractive.com/a/eu4/color-picker/ (Accessed: 26 October 2017).

Map modding – Europa Universalis 4 Wiki (n.d.) Eu4.paradoxwikis.com. Available at: https://eu4.paradoxwikis.com/Map_modding (Accessed: 26 October 2017).

“Master Modding Guides List” (2013) forum.paradoxplaza. Available at: https://forum.paradoxplaza.com/forum/index.php?threads/master-modding-guides-list.729388/ (Accessed: 26 October 2017).

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