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I'd like to overlay the cities of Europe on Australia for distance/size comparison purposes using QGIS and I'm wondering how best to achieve this while preserving distance between the European cities?

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    Perhaps a rudimentary method but I would use a projection CRS such as WGS 84, load the layers which contain European cities and Australia, then physically move all the features of the cities at the same time to overlay them with Australia. I'm sure there's nicer methods but I used this method when I did a very basic comparison test with several countries.
    – Joseph
    Commented Sep 11, 2015 at 12:54
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    @Joseph - this procedure will not preserve distance as requested by the OP -- Europe is at a much higher latitude.
    – Vince
    Commented Sep 11, 2015 at 13:22
  • @Vince - That's a good point, thanks for mentioning that.
    – Joseph
    Commented Sep 11, 2015 at 13:34
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    What about solving this through two overlapping map frames in print composer?
    – Miro
    Commented Sep 11, 2015 at 13:39
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    @Miro - I think you have the best solution and you should post it as an answer. I'll just add that he needs to use a conformal projection to preserve the distances.
    – Nahas
    Commented Sep 11, 2015 at 13:57

3 Answers 3

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It's somewhat roundabout, and I don't know how you'd implement it in QGIS, but I'd try:

  1. Flip the sign on European latitude values,
  2. Shift the Europe longitude to center on Australia,
  3. Define two conic projections using the same central meridian but different standard parallels for Australia and flipped Europe
  4. Override the flipped Europe projection with the Australian projection

From there, you might flip north to south through the central parallel, but the distances would be compromised by that process.

It would also be possible to flip longitudes about a central meridian in step 2, which might be less disorienting.

Finally:

  1. Either deproject the European shapes to GCS_WGS_1984 or project the Austrialian data to the conic projection for apples-to-apples comparison.
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If its just for presentations, i'd just overlay 2 images like this, if you need it as a vector just transform one of them with this plugin.

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If you are after some quick solution I made in few minutes overlap by using two map frames overlapping each other in print composer. All you need to do is keep same scale for both frames and remove background.

Oz vs Europe as two overlapping frames in print composer

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    Using an equal area projection centred on the middle of each continent? Commented Sep 11, 2015 at 14:18
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    @Vesanto I agree this is quick and dirty solution, but in this case with WGS84 roughly gives idea. I guess using Albers for Europe and Albers for OZ would be more precise but then QGIS unfortunately doesn't have yet option to have two frames in two CRS.
    – Miro
    Commented Sep 11, 2015 at 15:08

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