How to Install Map Mods Without Breaking the City (2026)

To install map mods without breaking the city, work in a fixed order: confirm the map matches your exact game version, copy your save somewhere safe, install the loader the map needs, drop the map files into the one correct folder, then test it in a throwaway sandbox city before touching your real save. Most broken cities trace back to skipping one of those five steps, and the whole routine takes about fifteen minutes.

The reason it matters is that a map mod does not just add scenery. It feeds terrain generation, the map theme, and often the climate when a world is created, so a mismatch does not fail politely with an error message. It hands you cracked ground, dead terraforming tools, or a crash the moment you hit play mode.

One more thing worth saying up front: the two games in this genre do not share an install method at all. Cities: Skylines uses Steam Workshop and .package files. Cities: Skylines II uses BepInEx and .cok files. Search results mix the two constantly, which is why so many players end up with a map that simply does not appear.

What You Need

You need four things before you start, and one of them is a spare copy of your city. The rest is the game itself, a way to place files where the game can read them, and the map files themselves.

• Your exact game edition and version. In Cities: Skylines, open the game through Steam and check your branch in the properties window. In Cities: Skylines II, note the build number from the main menu.
• A mod loader or installer. Cities: Skylines II needs BepInEx, and most players get it bundled with a manager like the Thunderstore app or rModMan. Cities: Skylines needs the Steam Workshop, or Content Manager if you are installing manually.
• A backup of the game folder and your saves. A separate drive is better than a folder inside the game itself.
• The map files, unzipped and read. Most archive problems happen before anything is installed, because the extractor created a folder inside a folder.

How you can tell whether a map supports your platform takes about a minute. On the mod’s own page, look for the game title in the header, the last-updated date, and any listed requirements. If the page was last touched more than a year ago and the game has had patches since then, treat it as suspect. The community on r/CitiesSkylines2 and r/CitiesSkylinesModding is blunt about this one: a map built against an old build is the most common reason a city arrives broken.

Here is the fork in the road that trips people up most often.

What differs	Cities: Skylines	Cities: Skylines II
Official mod support	Steam Workshop built in	None, everything is unofficial tooling
Map file format	.package files	.cok and .cok.cid files
Install folder	AddonsMods, or Workshop subscription	BepInExpluginsMapName
Typical manager	Steam Workshop or Content Manager	Thunderstore app or rModMan
Common breakage	Missing roads at the map edge, outside connections that do not snap	Crash 1-2 seconds after entering play mode, terrain seams at the border

If you are not sure which game a guide is written for, the file extension settles it immediately. A .cok file in Cities: Skylines does nothing at all, and a .package file in Cities: Skylines II is equally invisible.

How to Install Map Mods Without Breaking the City: Step-by-Step

Here is how to install map mods without breaking the city, in the order that keeps every step reversible. Do not skip ahead to the file copy. The check and the backup take less time than restoring a city.

Check the map mod’s compatibility first

Compatibility comes down to four things: game version, platform, dependencies, and known conflicts. If a map lists a dependency, that dependency is not optional, and installing the map without it produces exactly the kind of broken terrain this guide is about.

Open the mod page and read the description end to end before downloading anything. You are looking for the game it targets, the date it was last updated, and any other mods it needs. Then check the comments for the most recent posts. When a game patch lands, the first replies are usually people reporting that the same map now crashes, which is a faster signal than any changelog.

If you find nothing recent, do a quick search for the map name plus the word broken or crash. Players are remarkably consistent about the same three failure modes: terraforming gone, artifacts along the border, and an instant crash on entering play mode. A map with several recent reports of that kind is a skip, not a gamble.

Back up the original game files

Copy the whole game folder, not just the save. If a map mod overwrites a shared asset, the only way back is the original file, and reinstalling the game does not restore your cities.

For Cities: Skylines, the game folder is usually in your Steam library, and saves sit in the AppData folder under the game’s local data directory. For Cities: Skylines II, saves live in a similar user folder. The simplest reliable method is to close the game fully, then copy the entire install folder to a different drive or a clearly named folder somewhere else.

Confirm the backup before you continue. Open the copy, find your save, and check that the file size looks reasonable. A 0 KB save means the copy failed, and finding that out now rather than after a crash is the entire point of this step.

Take a screenshot of your mod list too. If something breaks later, knowing exactly which mods were active beforehand saves a long guessing game.

Install the required mod loader and dependencies

The loader goes in before the map, never after. In Cities: Skylines II that means BepInEx, which is nearly always installed through a manager rather than by hand: the Thunderstore app and rModMan both handle it, and both let you install and update maps from inside their own interface.

Install the loader, launch the game once so it writes its own configuration, then close it. That first launch is how you confirm the loader is alive, and it also generates the folders the map will go into. A manager that reports the game but shows no plugin list after a launch means something went wrong, and installing a map on top of that just moves the problem.

In Cities: Skylines there is nothing to install first. The Workshop is part of the game, and Content Manager handles manual .package files if you are not using Steam. If you use a manager there, give it the game folder and the local data path before you deploy anything.

Add the map’s dependencies now, while you are already in the manager. Installing a map and its dependency separately later is how you end up with two versions of the same map on disk.

Replace or add the map files correctly

Map packages come in three shapes, and mixing them is the second big cause of broken cities. Replacement maps overwrite terrain data and are the most likely to fight with each other. Additive maps add content alongside the base game and are safer to combine. Map-loader packages are bundles that bring their own structure and expect to be the only thing in their folder.

For Cities: Skylines II, the expected layout is a folder named after the map sitting directly inside BepInExplugins, with its .cok and .cok.cid files inside that folder. Some packages include a further Maps subfolder, and some launchers do not support subfolders at all. If the map does not show up in the new game screen, flatten it one level and try again. That single folder level is the most common CS2 install mistake.

For Cities: Skylines, drop .package files into the Addons folder inside the game directory, or subscribe through the Workshop and let Steam place them. Content Manager does the same job with a checkbox, and it is far easier to undo later.

Two rules protect you here. The mod author’s exact directory instructions always beat any guide, including this one, because the author knows what their package expects. And never combine files from two different map packages into one folder, because the game will happily load a mismatched set and produce a world with missing tiles and floating geometry.

Launch the game and test the city

Test in a new sandbox city, not your main save. This is the single most repeated piece of advice across the modding communities, and it is the cheapest insurance available: start a fresh game, pick the new map from the list, and let it run for a few minutes of play mode.

Check four things in that sandbox. The map appears in the new game list at all, which proves the files were found. The terrain renders without gaps or strange shapes at the edges. Terraforming and terrain modification respond when you try them. And the outside connections sit properly on the map border, since a map that loads but has dead roads around the rim will quietly wreck your traffic routing later.

If the game crashes one or two seconds after you enter play mode, that timing is itself a clue. It usually means a file loaded far enough to start the world and then hit a bad asset. Go back, check the version, and check for a duplicate copy installed by a second manager.

Once the sandbox looks right, you can think about your real save. Adding a map to an existing city is possible, but the map’s terrain does not overwrite terrain you already built on, so a map that changes the ground will only partially apply. Starting fresh is usually the cleaner result.

Restore the backup if the city will not load

Recovery is straightforward because you made a copy. Close the game, remove the map folder from BepInExplugins, and remove it from your mod manager’s list so it does not redeploy on the next launch. That second step matters, because leftover files in the plugins folder keep loading even after you think you removed the mod.

Restore your clean game folder from the backup copy and launch. If the original city loads and plays normally, the problem is the map, not your install. If two mod managers were running, clear both caches and keep exactly one copy of the map, then reinstall from a single source.

Then try a different version of the map or a different map entirely. After a restore and a clean retest, the answer is almost always a version match problem, and hunting further into a single broken package wastes time. The MapInstaller project is explicit that it has no automatic uninstall, so that manual cleanup is the intended path, not a workaround.

Common Mistakes

These are the failures players actually report, with the fix for each one. Read the symptom column first, because most people recognize their problem here before they recognize the cause.

Symptom	Likely cause	Fix
Crash one or two seconds after entering play mode	Map built for an older build, or a conflicting asset	Check the mod’s last-updated date, match your game version, install one version only
Trees standing in the ocean, odd valley shapes along the border	Map was re-saved without tile data, or theme files are duplicated	Reinstall the map fresh, delete duplicates, test on a new sandbox game
Terraforming and terrain tools do nothing	Map data locks the tiles, or a dependency is missing	Install the listed dependencies, start a new game, recheck the terrain panel
Map never appears in the new game list	Folder is one level too deep, or the wrong game’s file format was used	Flatten the folder inside BepInExplugins, confirm the extension matches your game
Roads missing at the map edge, outside connections dead	Map’s outside connection data conflicts with a replacement map	Run only one replacement map, remove competing terrain mods
Existing save will not load after installing a map	Map changed data the save already depends on	Restore the save backup and install the map before starting a new city
Everything broke after adding DLC	New assets invalidated the current mod setup	Uncheck all mods and assets, install the DLC, then re-enable them one at a time
Install appears to succeed but nothing changes	Wrong folder, read-only install, or a console-managed library	Run the game folder as administrator once, confirm you are editing the install the launcher points to

One prevention tip beats all the rest: install one mod, test it, then install the next. Players who add twenty mods and then work backward to find the culprit lose entire evenings. One at a time costs you a minute each and finds the problem immediately.

A second one is to keep a clean vanilla save that never has mods attached. Starting a modded city from a vanilla file is the fastest way back to a working game when something goes wrong.

Frequently Asked Questions

Conclusion

To install map mods without breaking the city, two decisions come before everything else: confirm the map targets your exact game and version, and copy your save somewhere outside the game folder. After that, the order is fixed. Install the loader, add the map files where the author says they go, and test in a throwaway sandbox city before opening the city you actually care about.

When something does go wrong, the fix is rarely mysterious. Remove the map folder, clear the manager cache, restore your clean copy, and try a different version. Keeping a vanilla save untouched is what makes that recovery take minutes instead of an evening, and it is the cheapest habit in this whole guide.

Updated for 2026.