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I have an image of a fiber optics network map:

enter image description here

I want to turn this map image (without any actual GIS data) into a vector map where each point is defined by lat, long.

To do this, I'm trying to import it in QGIS. I'm using the OpenLayers plugin to have Google maps as a basemap layer. I have an empty vector layer with projection set to EPSG:3857 where I want to draw the points.

I can't import the image and position it correctly over the Google Maps basemap.

As suggested, I tried this tutorial, placing 5 points (4 at the edges and 1 at the center).

I import the map guessing the coordinate system to be `Any idea what projection was used to create that map?

I tried both pasting coordinates in this format 48.767479, -97.551781 (found on Bing Maps searching the name of the cities) and in this format 48 46 02.92, -097 33 06.41 found using this converter.

In both cases, I end up with a super small, distorted map off the coast of Gabon.

I also tried picking coordinates from this webpage instead, which gives me projected coordinates in EPSG:3857, and feeding them to the Georeferencer plugin worked. However, my image is now very distorted when shown on top of the Google Maps (or Bing Maps) layer.

I guess the projection is not Mercator. Any idea on how I can work on this map without the distortion?

Stretched image on map

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    I can see this might ask the same question. But the answer to that question is 3 lines long and links to an off-site tutorial that has been "moved" somewhere else. And that tutorial deals with placing polygons instead of lines. Oh, and it does not explain how to stretch the image over Google Maps, but assumes I know the coordinates of some points of my map already. Mhhh, not what I need?
    – Agostino
    Jun 28, 2015 at 18:46
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    If you edit the question, and explain why that is a different issue, it will likely be reopened.
    – BradHards
    Jun 29, 2015 at 9:55
  • The 'moved' tutorial had a link right at the top of where it moved to. I've updated the answer to give the new link as well. Bottom line, you are trying to georeference an image as a first step to then digitize the information on it. The tutorial explains georeferencing. The difference between creating lines and polygons (or points for that matter) is trivial - the point is you'll be drawing on top of the image. Also note Google Maps uses a projection/CRS (EPSG 3857, Web or Psuedo Mercator, lower right corner of your screenshot) that isn't well conducive to creating data.
    – Chris W
    Jun 29, 2015 at 19:11
  • @ChrisW I edited this with my attempts to follow the tutorial. No luck, I must be doing something wrong.
    – Agostino
    Jun 29, 2015 at 22:46

1 Answer 1

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Your last attempt looks very promising. With more than 5 points you might get an even better picture.

I use this transformation settings:

enter image description here

Using as many border points as possible for georeferencing, I take the coordinates from the map canvas with the middle icon:

enter image description here

and get this picture (with clipping to GADM borders):

enter image description here

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  • Thank you. I added more than 10 points, but I still can't get it to match the Google Maps borders very well. I used EPSG 3857 coordinates to open the image in the Georeferencer plugin, set the points and to export back to QGIS them. It's the only combination that somehow worked (maybe it's a plugin bug, for other coordinates it sometimes crashed too). After doing this I tried changing the project properties. Is it too late now?
    – Agostino
    Jun 30, 2015 at 8:10
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    It might help if you take the border points from the google map background to georeference. EPSG:3857 is correct for that. The city points might be the point of the fibre optic network switch, and not the town center.
    – AndreJ
    Jun 30, 2015 at 9:20
  • I'm confused. Is there a way that I can specify the points using EPSG:3857 and then work on the map without distorting it? Is there a chance to use a basemap that matches the projection used in the image? Thanks.
    – Agostino
    Jun 30, 2015 at 9:43
  • The Georeferencer offers you an icon labelled From map canvas. All you have to do is search for the point on the base map, and click on it (and set the CRS in Settings -> Transformation Settings to EPSG:3857 as well).
    – AndreJ
    Jun 30, 2015 at 11:11
  • I can't find any icon labelled From map canvas in the Georeferencer. Your results seem better than mine (my map is more distorted). I set the project CRS, the map layer CRS to EPSG:3857. I set EPSG:3857 when importing the image in the Georeferencer and when exporting it in the Transformation settings. However, your results look better than mine. Could you provide a download link to the project and\or the GCP points you used in the Georeferencer? The georeferenced .tiff image would be OK too (maybe you can 7zip it to prevent the host from messing with the upload). Thanks.
    – Agostino
    Jul 6, 2015 at 17:56

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