At Using/synonymizing/merging [coordinate-system] and [projection] tags? we synonymized a number of tags related to coordinate systems.

Today I noticed Re-projection issues with Azimuthal Equidistant with tags for and .

Are both or either of these tags necessary, or could one or both be synonymized with another tag?

2 Answers 2


Following the line of the synonymization between and , I would agree to synonymize and to as well.

Mainly because I think they should be synonymous with .

The terms are not synonymous. However, I don't think synonymous tags should necessarily refer to synonymous terms.

What I would find useful is to add in the definition of that the tag:

also applies to projective geometry and coordinate system transformations.

I think that it would be resolved that when a user writes projection in the field of tags, he/she note that everything related to projections and reprojections is labeled as , which after all is very useful to group in that way all the questions that refer to the coordinate systems in which geographic information is analyzed and represented.

It occurs to me that the description or definition of what a coordinate system is, is not enough to describe the tag:

A reference framework consisting of a set of points, lines, and/or surfaces, and a set of rules, used to define the positions of points in space in either two or three dimensions.

And that adding a phrase referring to cartographic projections and coordinate system transformations could help describe the tag and its synonyms.

It may be convenient to open a new question about this idea. For now it is raised here and in the chat.

A wiki edit was submited for approval, wich includes the phrase:

This tag also refers to cartographic projections and coordinate system transformations.

  • 2
    These have now been made into synonyms with a view to merging them later.
    – PolyGeo Mod
    Commented Nov 11, 2019 at 21:58
  • While I very much agree that projection-mathematics and reprojection-mathematics are synonyms, I very much disagree with making them synonyms of 'coordinate-system'. Someone with a genuine interest in reprojection mathematics could previously very easily identify 96 questions. Now they have to wade through 5,869 questions. What benefit does this bring?
    – JimT
    Commented Nov 22, 2019 at 9:58
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    @JimT Among those 96 questions at least two are the same, which generated this post: gis.stackexchange.com/questions/341044/… .Which showed an inconsistent use of those tags (. Someone with a genuine but exclusive interest in the mathematics behind a reprojection would not be interested in that question). The benefit that synonymization brings is to avoid the inconsistent use of tagging. Commented Nov 22, 2019 at 11:01
  • Misuse of a tag in an anecdotal incident is no argument against generalizing so much that nothing can be found for a particular subject - and in this case I already agree the two mathematics tags should be synonyms. I have an interest in re-projection mathematics, and I imagine others do too. How do I now narrow a search down from 5,869 questions?
    – JimT
    Commented Nov 22, 2019 at 11:37
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    @JimT a comment won’t make your case but an answer might. A synonym is easily backed out if the community supports your proposal but when a synonym proceeds to be merged that tag is totally removed from the questions that had it.
    – PolyGeo Mod
    Commented Nov 25, 2019 at 3:17
  • @PolyGeo Maybe I don't understand the merge process, I can't search for questions with the [projection-mathematics] tag right now (is the synonym already merged?) but I can see that tag in some questions of the following search: gis.stackexchange.com/… Commented Nov 25, 2019 at 3:49
  • @GabrielDeLuca This is worth reviewing: meta.stackexchange.com/questions/70710/… A synonym treats the original tag (which still exists on questions) as if it were the master synonym whereas a merge removes the original tag from all questions.
    – PolyGeo Mod
    Commented Nov 25, 2019 at 4:05
  • @GabrielDeLuca We merged a lot of our synonyms a bit over a year ago via gis.meta.stackexchange.com/questions/4905/…
    – PolyGeo Mod
    Commented Nov 25, 2019 at 4:06

Agree completely with making tags projection-mathematics and reprojection-mathematics synonyms with a view to eventual merging. The two terms are identical.

While I further agree the subject of these two tags is indeed a sub-class of the wider 'Coordinate-System' tag, I disagree with any further synonymization.

There is a significant quantity (>5,500) of questions with coordinate system tagged. Following synonymization, anyone with a genuine interest in reprojection-mathematics (~100 questions) would really struggle to filter that list down if so desired.

There is a danger here of generalising tags so much that less popular (but not less important) subject areas are eclipsed.

TL;DR: Merge the two tags. No further action required.

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