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Thread: Best projection for overlapping regional maps?

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    Guild Member laevex_esre's Avatar
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    Question Best projection for overlapping regional maps?

    I've almost finished creating my world map, here.

    Next I want to get working on mapping each region of the globe in some detail. I've tried this before and found that any overlap between such maps is extremely difficult. Is there a good projection to use for this purpose? Almost every projection type distorts the geology as far as I can tell, making it very difficult to overlap maps. I'd love to know if there's an answer to this.

    Or am I doomed to painstakingly redrawing all of the cities and roads of my maps?

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      feanaaro is offline
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    isn't the classical mercator, or perhaps equirectangular, good for this purpose?

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    Guild Member laevex_esre's Avatar
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    Equirectangular distorts distances quite a lot from what I can gather off the internet. Mercator might not distort so much, but atlases usually use Lamber Azimuthal Equal-Area projections these days. The problem with these is they won't overlap very well. Maybe Mercator is my only shot?

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      moutarde is offline
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    All map projections distort distance to some degree. Do a wikipedia search for map projection, or ask Hai-Etlik or Cantab on these forums for advice.

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      cantab is offline
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    Well two different map projections, in general, aren't going to line up - if they did then they'd be the same projection.

    gdalwarp will translate images from one projection to another. However, using it from the command line may be tricky. QGIS lets you call it and then you can select projections from a list of standards. (You may need a plugin, I'm not sure.)

    What sort of size regions do you plan on working on?
    I am a geology nerd.

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      Hai-Etlik is offline
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    To get maps to "line up" that way, you need to be using the same projection for all of them, and pretty much the only projection that looks any good "zoomed in" that way is Normal Mercator, which is still far from perfect. That's why real maps are done in projections appropriate to their extent and purpose.

    You might want to look into vector graphics, and vector GIS tools if you want to be able to reproject data and then symbolize it. Inkscape is a good vector graphics editor, and for a GIS you might try QuantumGIS, uDig, or OpenJUMP.

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      cfds is offline
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    Distortion is always a function of the extent of the map relative to the globe. You can map a whole planet with lots and lots of small equirectangular or Mercator maps, centered on the region in question. They will never overlap perfectly but good enough.

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    Guild Member laevex_esre's Avatar
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    OK. That's all interesting. How do you guys think HandsomeRob did the overlap in step 4 of this tutorial then? He was using a Lambert Azimuthal Equal-Area projection, which is quite a nice one I think.

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      cantab is offline
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    I think all his maps are just in the exact same projection. That's suitable for mapping regions of a continent, but it may not be ideal for a whole world. (It might be OK if you don't want regional maps of the poles.)

    LAEA is good close to the projection centre, distortion being about 2% within 15 degrees, 5% within 30 degrees, and 10% within 45 degrees. The further out one gets, the more squashed the map becomes; by the time you reach 90 degrees (half the planet) it's up at 25%, equivalent to turning a square into the shape of a widescreen TV.
    I am a geology nerd.

  10. #10
    Guild Member laevex_esre's Avatar
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    If HandsomeRob's regional maps are from the same projection, why don't bits of them look horribly distorted? His continents are huge.

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