Minimaps can be constructed and rendered through the Map Tab in Dev Mode. The map tab has four different editing modes: Canonical View, Subregion View, Attractiveness View, and Dev View. For minimap editing, you want to be in the Dev View.
While in Dev view, click and drag a room to reposition it. Click and drag anywhere else to scroll the canvas around. While holding the N key, click a room to change what layer it is in. There are three layers, green being the closest, grey being the middle, and red being the furthest back. In general, you should avoid overlapping any rooms that are in the same layer as each other. Overlapping rooms that are in different layers is fine.
You can click the Save button to save your changes. You should do this periodically to avoid losing any progress. When you are finished positioning all the maps how you want them, click the Render button to generate the final minimap. (This render step tends to fail a lot, see the troubleshooting section below for solutions)
When rendering the minimap, sometimes it will fail. It will either generate a completely empty map (the rendered map image will just be an empty green rectangle), or it will generate a map, but all the map interconnections will be undefined (when you view the minimap, the dotted lines that connect the rooms will either be missing, or will curve all over the place randomly).
Here is the most reliable procedure I've found to have success in rendering the final map:
- When you are done making your changes, hit the save button, but do not hit the render button.
- Exit the game, and either start a new save file, or revert to a save file from before you entered the region for the first time.
- Enter the region fresh, and as soon as you enter the region, go to dev mode, open the dev view map and render it.
- The map should be correctly rendered now.