Region to Skylines

Drag the map: the square stays in the middle

Rotate 0° Real ground on the map Height Cut OSM rivers and lakes

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Height x3 · drag to orbit

The game cuts the map into 9 x 9 tiles of 1.92 km. The base game lets you build on the middle 25 (9.6 km square), unlocked one at a time as the city grows; you start on the centre tile. The 81 Tiles 2 mod opens all 81 (17.28 km), and can unlock them all at once. The heightmap always covers all 81.

Make it buildable

Smooth terrain Removes survey and tile-seam noise that makes jagged slopes roads can't follow. River depth Deeper beds hold water and keep it from spilling into the valley. River width Wider channels flow more steadily; the game's water needs room to spread. Lake depth Lakes are sunk flat below their shore so a water source can fill them.

Water sources for the Map Editor

The heightmap carves the river and lake beds; for now the Map Editor adds the water. Suggested spots, in the editor's coordinates (metres from the centre, x east, z north). Which way each river flows is read from the ground.

Waiting for rivers and lakes…

Map name

Have Claude Code, Codex or another agent with a terminal do the setup: paste what this copies. It links this square and the agent instructions; the agent runs one command that builds the same heightmap and puts it in the game's folder.

Put it in the game

Save the PNG into the game's heightmap folder:
- Windows: %LOCALAPPDATA%\Colossal Order\Cities_Skylines\Addons\MapEditor\Heightmaps
- macOS: ~/Library/Application Support/Colossal Order/Cities_Skylines/Addons/MapEditor/Heightmaps
- Linux: ~/.local/share/Colossal Order/Cities_Skylines/Addons/MapEditor/Heightmaps
Start Cities: Skylines, open Tools → Map Editor, make a new map, and pick your file under Import heightmap.
Sea level. Coastal maps: set it to the value under “Sea level in game” above. Inland maps: drag it below the lowest riverbed (under “In game” above) so the valleys stay dry.
Water sources. Under Water, place one source on each dark blue pin (where a river enters or starts) and one in the middle of each lake (light blue pins); positions are under “Water sources for the Map Editor”. Grey pins mark where a river leaves: put nothing there.
Starting tile. It must have water and a highway in and out (Map Settings → Start Area moves it). Draw highways from the map edge along the real ones.
Playing with 81 Tiles 2? Disable it before opening the Map Editor; the mod turns the editor off because it breaks saved maps.

The file is 1081 x 1081 px, 16-bit greyscale, 17.28 km across, with black = 0 m and white = 1024 m. The lowest ground sits at 50 m so water has room below the land; when the relief is too tall for 1024 m, heights are squeezed to fit (shown under “Height”).

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