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This is meant as some kind of reference Q&A.

Unless I am working with truly global data, I always prefer projected, local, metric coordinates so that calculations like area or distances are "right by default" in tools like QGIS. So if I get original data for a country in its UTM zone's coordinate system - perfect!

Many people highly prefer getting their data in WGS84 (4326) or Web Mercator (3857) for ease of use in tools like Google Maps.

I just read a open data release suggestions catalog and publishing geodata in those systems was one of the items. This made me wonder:

Apart from convenience, are there any drawbacks of using one or the other?

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I always prefer coordinates in latlon WGS84 because they are usable worldwide and easy to understand once you know which is latitude and which is longitude.

I happen to live in a country that spans across several UTM zones, and before that used several smaller Gauss-Krueger zones. As long as you are within one zone, everything is ok, but cross-zone computing always leads to trouble.

Apart from that, many old projected CRS have datum shifts of up to hundred meter. WGS84 is on the safe side to avoid additional datum shift misunderstanding. Unfortunately, some countries had adopted UTM with different datums before WGS84 was established. So you have to ask for UTM zone, ellipsoid and datum.

Web Mercator is nothing worth but a popular visualization: http://www.hydrometronics.com/downloads/Web%20Mercator%20-%20Non-Conformal,%20Non-Mercator%20(notes).pdf. You should not try to measure anything with it.

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From a visualization point of view I was though you should use projected coordinate systems for even things on a US State size scale. Any size State that is broken into multiple State Planes, looks best in a Web Mercator or WGS projection. When you get to a region or city level, most data looks a little better in a state plane or utm projection.

  • My question is about the raw data, not maps that users might build with them. Maybe that is not clear enough? Please say so. – bugmenot123 Jul 31 '15 at 14:47
  • I guess it wasnt clear to me, but it is quite early in the morning. – ed.hank Jul 31 '15 at 14:58

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