[PROJ] Why is Web Marcator EPSG:3857 so popular for web maps (vs EPSG:4326)?

[Lesparre, Jochem]

Hi Idan,

I would like to point out a few issues:


  *   WGS84 is not a projection, therefore it has no projection distortions. The world is an ellipsoid in WGS84, not a rectangular map. The deformations you refer to is what you get when ones uses the platte-carée projection (x=longitude, y=latitude) as for instance QGIS does by default. Google Earth instead uses a globe for WGS84, so it has (almost) no distortions.
  *   EPSG:4326 is a bad choice for a CRS, as it is 2D and because it is a datum ensemble. It is better specify a specific reference frame (e.g. WGS84-G1761). Or even better: to use the official international terrestrial reference system (e.g. ITRF2014) in stead of a CRS defined by the military of one random country.
  *   Web Mercator is an approximation mixing spherical formulas and ellipsoidal coordinates. Therefore it is not conformal. True Mercator is a better choice as it is conformal. I do not believe the more complex computation is a real problem for modern computers.

Kind regards, Jochem

From: PROJ <proj-bounces at lists.osgeo.org> On Behalf Of Idan Miara
Sent: donderdag 26 november 2020 14:47
To: PROJ <proj at lists.osgeo.org>
Subject: [PROJ] Why is Web Marcator EPSG:3857 so popular for web maps (vs EPSG:4326)?

Hi all,

I was wondering if you can enlighten me regarding why Web Marcator (EPSG:3857) is so popular and used by virtually all major online map providers as opposed to WGS84 lat/lon (EPSG:4326)?

I've composed some points that I could think about, but it doesn't add up for why 3857 maps (i.e. slippy map) are more popular than 4326:

1. In 3857 almost all the world fits in a rectangular tile (~85 deg north to ~85 deg south), which makes it easier to divide the tile further into sub tiles.
In 4326 all the world fits into two rectangular tiles (so not much more complicated, I guess).

2. Users expect coordinates in 4326 and the transformation from 3857 to 4326 is rather fast (in comparison to ellipsoidal mercator).
But if you save the coordinates in 4326 then you wouldn't need to transform at all.

3. 3857 is "almost" conformal - I think that the normal use case is not marine navigation so it doesn't seem so important.

4. Both 3857 and 4326 have size distortion.

5. You can't measure distances, areas or angles easier in 3857 as far as I know.

What am I missing? Is 3857 faster or more useful in any other way than 4326?

Kind regards,
Idan


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