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I want to use QGIS to georeference two fantasy (D&D) raster maps, one is the map for the entire world (Toril), one is the map for one of the continents (Faerun).

This is the post with the world map. enter image description here

This is the website with Faerun map. enter image description here

I have already aligned the continent map to the world map in gimp, and marked the corners on the world map where the continent map should go (in order to be able to easily find them on the georeferencer plugin). I have also recentered the whole map to have the equator and the prime meridian at the center of the image (I don't know if this was needed).

This is the result.

enter image description here

Now I would like to import both of them in a QGIS project and (sorry for improper terminology) place them on a sphere/world.

I need to specify a projection, but I have no idea what kind of projection I am looking at in the world map, and I also think I need to create a .pngw file to tell the georeferencer plugin about the measures in this map, but it's not clear how should I calculate the needed values. For the moment we can assume that Toril has the same size of Earth.

I have already seen this question Get correct measurements for fantasy world map but I am starting with only two raster images with no georeference data of any kind.

How should I proceed?

  • Are you sure that the world has a closed suface (can you cross the poles and/or the antimeridian)? How do you know where is the equator or the prime meridian located (do you have geographic coordinates)? Is the fixed scale of the map the scale at the equator or/and the central meridian or/and the entire map? – Gabriel De Luca Mar 14 at 13:03
  • @GabrielDeLuca yes The world map represents a closed surface (if you go all the way to east on the image you will re-enter from the west side, same thing if you go north). Prime meridian and equator are centered in the image in my modified version imgur.com/a/Qxv4AdH. I did not understand your question about the fixed scale. – yann.kmm Mar 14 at 13:16
  • If you go north and you can cross the map to the bottom of it, the world has a torus shape. On a map of a spherical world, if you cross a pole you appear 180 degrees on one side, not on the opposite pole. It seems to me that your world is flat, with a mathematical device to give continuity to the edges. – Gabriel De Luca Mar 14 at 13:29
  • @GabrielDeLuca oh yes you are right, I can confirm that it does not have a torus shape (wrapping my head around those concepts is for me as difficult as wrapping the map around the world =) – yann.kmm Mar 14 at 13:33
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I suppose there are many ways, personally i would georeference the image to the real world. Here is a tutorial of how to georeference data in qgis, you can just follow the example of the "scanned image", which is basically the same what you got, a plain image without geographic data.

You might need some real world imagery to georeference to, the open street map would be fitting i guess. Here is a tutorial. When using web maps like the OSM, your Map Coordinate System will be EPSG:3857, which should be fine, you can still reproject your data later, for instance if you need spherical coordinates (lat/long)

  • Hi Rob, thanks for the quick reply, how should I georeference an entire map of the world if I only have equator and prime meridian? The first tutorial you linked is what I will do with the Faerun continent map, but first I need to have the word raster image imported and georeferenced correctly (this is the role of the pngw file I suspect, and I don't know exactly how to calculate its values). – yann.kmm Mar 14 at 12:23
  • well, you can just georeference the corners of your map to the corners of the OSM background. Although looking at your design, the fantasy world looks quite flat, the maybe you forgot the distortion around the poles... the problem is this, i suppose you want your design to be flat, so distances are the same everywhere, right? because if you drape your design on top of a sphere, real world distances vary quite highly. For instance, your scale bar will only be true at one specific latitude (probably the equator) – Rob Mar 14 at 12:53
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    I would just try to get the OSM into your QGIS, and then georeference your image to that background, with the width of your image being the width of the OSM, and the height being whatever looks plausible to you, keeping distortion as low as possible – Rob Mar 14 at 12:55
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    I think we can assume that the distances are equal everywhere on the world map, I understand your comment referring to the changes in scale, I will try to do as you suggested and see what results I get. (even if I don't yet know how to deal with the poles) – yann.kmm Mar 14 at 13:36
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    one simple solution (depending on your use case) would probably be just to add 20% waterbodies to the top and the bottom of your map. This might look a lot on your image, but is actually quite little in real-world units. Your image of your fantasy world is most likely closest to a mercator projection, you can see how the pole distortion works here: en.wikipedia.org/wiki/Mercator_projection#/media/… – Rob Mar 14 at 13:50
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This is how I did it, following @Rob's suggestion in the comment:

"I would just try to get the OSM into your QGIS, and then georeference your image to that background, with the width of your image being the width of the OSM, and the height being whatever looks plausible to you, keeping distortion as low as possible"

Instead of using the osm map, I used the continents shapefile found here (which looked more like the map I was trying to import):

Toril is a fantasy world, and there are only approximate measurements, so I have made the following assumptions:

  • Toril is equal to Earth
  • the world/continent raster map are all correct
  • even if a map of a smaller region does not exactly align with the map of a larger region, the smaller region map contains the correct measurements

this way I can ignore the fact that a smaller region map does not align perfectly in all its features with the bigger map.

The continents shapefile has the following extents:

-179.9999999999000408,-55.9147779275592711
180.0000000001000444,83.6343268907734227

The Toril World map (after cropping the black bars at the top and bottom) is

16000 x 7240

I used the georeferencer plugin to reference the corner points of the raster map to the corner points of the continents shapefile, then manually corrected the point data using the extents and the pixel sizes, and I got the following georeference points:

-179.99999999990004085,83.63432689077342275,0,0,1
180.00000000010004442,83.63432689077342275,16000,0,1
180.00000000010004442,-55.91477792755927112,16000,-7240,1
-179.99999999990004085,-55.91477792755927112,0,-7240,1

And this is the final result exported from qgis:

enter image description here

  • You might want to add a grid and label it with lat/long. Then export it as an image with the labelled lat/long lines and share with anyone else who might be using the same world. That way you establish your lat/long grid as the canonical coordinate system for Toril. Otherwise, you run the risk that someone else creates a conflicting map. – csk Mar 18 at 17:24
  • Is there a way you might export this to Google Earth and share it? – Mox Mar 18 at 18:26
  • @csk, that's a really interesting suggestion I'll do it and update the images in the post. You think it would be enough to just make them visible in qgis and then exporting the png again? – yann.kmm Mar 19 at 10:22
  • @Mox, I have no idea if there are legal issues on doing that, if there are none I'm more than willing to share what I have done. As a counter-proposal, would you be open to the idea of working toghether on the qgis project I have started? – yann.kmm Mar 19 at 10:26
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    @Mox this is the correct link to the rpg site rpg.stackexchange.com/questions/143463/… – yann.kmm Mar 20 at 8:25

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