Creating large world maps in Cities: Skylines is always a special challenge because the terrain.party tool can export at maximum heightmaps of large cities. In order to represent an entire continent however, I use OpenStreetMap, which has a simplified representation at wide zoom, which benefits me for my use case.

Fast Grid

In order to speed up map making significantly, I created a transparent grid, such as that from terrain.party. I can now resize it and place it exactly over the location of the map that I would like to have as a map in Cities: Skylines.

As usual, the grid consists of an inner quadrant (25 fields), which represents the usable fields of a map. The outer, thinly drawn fields are only available with an 81 tiles mod. This would make it possible to build on the entire map.

The grid of a map in Cities: Skylines.
Heightmap was quickly created

In no time, the grid was correctly positioned on the map. I edited the screenshot a little so that the map is properly displayed in the editor. Thanks to the self-made grid, the heightmap was quickly created:

Heightmap of the Asia map.

In the making-of video, you can watch how this heightmap evolved into the finished map: