I've been searching through several web pages and haven't found an answer. I work in QGIS, usually with EPSG:25830 because my projects are mainly located in Spain but when representing a larger area I find it difficult to choose the best option. I was wondering if there's something like a web page where you can set the extent of your project so it suggests you the best options? I've been unable to find such a thing in the epsg.org web page, for example.

In QGIS, according to QGIS Documentation, the CRS Selector "gives you a rough preview of the geographic area for which a selected CRS is valid for use". For example:

enter image description here

Given that there are hundreds of different CRSs and not all of them have a self-explaining name or description, selecting them one by one and have a look at the area that they best cover is not an option. So what I was looking for was a kind of a "reverse" system, i.e. where you could set the extent of your project and it gave you back a list of suggested CRSs. Something that could help in answering questions like "which are the best CRSs to create a map for the Mediterranean basin?".

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    What means "best"? This very much depends on the goal of you map. Do you want to "best" reperenst areas? Or angles? Or shapes? For what extent? There are a lot of questions and it depends on each of them what projections fit this criteria.
    – Babel
    Mar 28 at 7:05
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    Of few ressources: pro.arcgis.com/en/pro-app/latest/help/mapping/properties/… - geo.hunter.cuny.edu/~jochen/gtech201/lectures/lec6concepts/… - source.opennews.org/articles/choosing-right-map-projection - map-projections.net/singleview.php - Best and ideal map projections; projections satisfying given conditions of representation, Chapter in : Lev M. Gugayevskiy, John P. Snyder: Map Projections. A reference manual. London 1995, pp. 93-228
    – Babel
    Mar 28 at 7:12
  • For a large area perhaps EPSG:3857, Google Web Mercator would be a good choice epsg.io/3857, it looks like there's a transformation from ETRS89 to WGS84 available. Being a well used CRS integrating online data should be easy.. just don't expect distances or bearings to be precise. Mar 28 at 7:17
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    EPSG:3857 has the advantage of being well supported online - but that might be one of the few if not the only advantage... Mercator projections for many use cases are not ideal. Angles (bearings) and shapes, however, are preserved. But that is helpful for (sea) navigation (in 16th century, using compass)
    – Babel
    Mar 28 at 7:22
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    EPSG.org allows map search to find relevant EPSG codes (others may exist from other authorities ESRI. OGC...) epsg.org/search/map but only you will be able to determine what's best.
    – nmtoken
    Mar 28 at 9:00

1 Answer 1

  1. Go to https://epsg.org/ and define your region of interest, e.g. using box and drawing a rectangular polygon:

    enter image description here

  2. You get a (long) list of CRS valid in the defined region.

  3. Decide what kind of projection you want: projected CRS or geographic CRS? You want to preserve area? Or angles/bearings/shapes? Or a compromise? See these resources for help:

  4. Go back to step 2 with the criteria identified in step 3 to see which of the projections fulfill these conditions.

  • OMG! I didn't see the search combo-box. That's exactly what I was looking for and it was right under my nose. Thank you.
    – jpinilla
    Mar 28 at 13:27
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    Maybe placing a point somewhere in the Mediterranean instead of using a box is better as a point does not cover many "national" CRS that are not useful for your purpose.
    – Babel
    Mar 28 at 13:29

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