Cities: Skylines: How to get a high resolution overlay map for Cities Skylines (Up to 90k px * 90k px))

Hi Citybuilder, if you have ever done a 1:1 rebuild you have probably used an overlay.
I started one in the past but was unhappy with the overlay resolution. At that time I did a merge of 81 maps together for a better result. But it was not very efficient.
I’ve found a better method. Here is how.

First of all, let me give you something to compare.

Here is the ‘default’ from ‘https://terraining.ateliernonta.com’ (skydark and terrainparty are down, so this is the way for height maps today)

The overlay has a resolution of 2160 x 2160px.

With this method you can get overlays with a resolution of 10k x 10k px (this is the limit of what Cities Skylines can handle).
You can also split the overlay or use only the inner 25 tiles/9 tiles for the overlay. If you use an overlay for each tile, you get a theoretical resolution of 90k x 90k px.
But enough talk, here are some examples (I recommend to open them in a seperate tab to get a better impression)

The 10k x 10k image when stretched across all tiles. Link to the picture: https://imgur.com/tRldYNn.png

The 10k x 10k image when stretched across 25 tiles. Link to the picture: https://imgur.com/WEzNDEt.png

The 10k x 10k image when stretched across 9 tiles. Link to the picture: https://imgur.com/N6r3maE.png

The 10k x 10k image when stretched across one tile. Link to the picture: https://imgur.com/RtvE2Bn.png

(Note: all examples are zoomed in to samle location)

To get such detailed pictures you have to do a few things. So let us start.

Download Qgis https://www.qgis.org/en/site/forusers/download.html

Qgis is a GIS software whose purpose is to create informative maps from geodata. But don’t worry, we don’t need to tinker with geodata.

After downloading, run the installer.

Now you should have a folder on your desktop called ‘Qgis 3.x’, open it and run ‘Qgis Desktop 3.x’ (x = the version number, in my case it is 23.3′).

After opening Qgis, create a new project by clicking on the blank page.

Now you need to install a plugin. To do this, click on ‘Plugins’ in the top menu and select ‘Manage and install plugins’.

In the plugin manager, go to the ‘All’ tab, search for ‘QuickMapServices’ and install it.

Then click on ‘Web’ in the menu at the top and navigate to ‘QuickMapServices’ > ‘OSM’ > ‘OSM Standard’.

Now it should look like this

(You only need to do this if you need an exact positioning of the overlay (e.g. if you also use a height map).

First you need the coordinates of your point. If you are using terraining.ateliernonta, you will find them in the top left hand corner.

Now go to https://coordinates-converter.com and enter the coordinates. The terraining.ateliernonta coordinates should be in the decimal degrees field.

Write down the UTM coordinates.

Then go back to Qgis scroll to your location and click on EPSG in the bottom right corner.

Now enter ‘WGS 84 / UTM zone’, that gives you a list of a few EPSG you need the one that has the number from the coordinate converter. If your place is in the northern hemisphere then you need the one with the N and if its in the southern hemisphere the one with the S.

Select the correct EPSG and press ‘Anwenden’ (for some reason some terms are in German) and the ‘ok’.

For my example pictures I have used Berlin. Berlins is in the northern hemisphere so the zone is 33N

In the bottom bar you will also find the coordinates window. Delete the existing coordinates and enter the coordinates from the converter, but only enter the numbers before the dot and separate both numbers with a space. (Don’t move the mouse while entering the coordinates)

Don’t move the map after that. If you have done this by mistake, enter the coordinates again. Moving your mouse will also change the coordinate but that’s fine. Just don’t move the map.

Now go to ‘Project’ > ‘New Print Layout’, enter a name and press ‘ok’.

Before we can continue, you need to think about the resolution you want and the size of the overlay. Here’s a quick overview (the last two are only possible if you split the overlay map into smaller pieces)(and don’t worry about the last 2 columns for now, they’ll be important later)

Once you have decided on the size of your map, you need to prepare it.
Right-click on the blank sheet of paper you see and select ‘Page properties’.
Enter the size you have chosen in the table above (Make sure you have selected the correct measurement).

Now it’s time to add a map (this is what you do for numbers 1-4). Click on the 5th icon on the left and then do a left-click on the paper.

Enter the image size for Width and Height. The X and Y values should be 0 and the reference point should be the top left corner.

The map will now be rendered and an item properties window should pop up. Here you change scale of the map.

Now it’s time to export the map. Click on the icon to the right of the print icon.

You may get a ‘WMS layer’ or ‘size’ warning, but you can ignore it.

Now choose the export parameters.
Choose 10000px for width and height and hit ‘speichern’.

If you want to use method 5 or 6, you have to do a few extra steps.

First, go back to the map and zoom out so that you can see roughly what the map would cover. (Remember not to move the map)
In the top menu, press ‘Processing’ and then ‘Toolbox’. A menu should appear on the right. Expand the ‘Vector creation’ menu and click on ‘Create grid’.
Change the grid type to ‘Rectangle (Polygon)’ and enter 1920 metres (if you want number 6) or 5760 metres (if you want number 5) for the vertical/horizontal spacing.
Next to the empty ‘Grid Extend’ box, you will see an icon with a mouse pointer, click on it and run the process.

Your map should now be covered in rectangles.
Next, left click on the ‘Grid’ layer and press f7. Then right click on the ‘colour’ on the right and change the opacity to 0.

Now click on the pencil icon (‘Toggle Editing’) and then on ‘Select Features by Area or Single Click’. Select all the tiles you don’t want on the final map. (Hold Shift to select multiple tiles)
Finally, delete the selected areas and confirm.

Click the pencil again and switch back to the print layout. Add the card by clicking on the 5th icon on the left.

Enter the width and height of the image. The X and Y values should be 0 and the reference point should be the top left corner.

Now click on ‘Atlas settings’ on the right, select ‘Grid’ as the coverage layer, choose ‘id’ as the page name and disable Single file export (you can hide the grid on the tiles with the ‘Hidden coverage layer’).

Then scroll down in the ‘Item properties’ to ‘controlled by atlas’, enable it and use the ‘best fit’ option.

You’re almost there, now it’s time to export the tiles. Click on the icon on the left of ‘Atlas properties’ (if you see a ‘WMS layer’ or ‘size’ warning, you can ignore it).

Select a folder to export the tiles to. Choose a resolution of 10000px for width and height.
It may take some time to export all the tiles.

Image overay mod.

First you need to subscribe to the ‘Image Overlay Renewal’ mod
https://steamcommunity.com/sharedfiles/filedetails/?id=2616880500

Enable it and load the game.

After loading the city, go in the game options and switch to the Image Overlay Renewal settings to open the png folder

The file explorer will open. Place here the exported overlays. (don’t creatre a sub-folder)

Now open the image overlay mod, reload the textures (click the button once and let it load a moment, don’t click anything or it might crash), select the map, size and position.

If you have used number 5 or 6 you might have to use an offset for each tile. Here are the needed offsets. (for number 5 you only need the bold numbers)

And thats was it. I hope all is clear but if you have questions problems or feedback feel free to bing me on the officieal Cities:Skylines Disord server. (My username is Link0610).

Otherwise I wish you fun with your recreations.