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

[Idan Miara]

Thank you all for your very detailed explanations!

On Thu, 26 Nov 2020 at 16:53, Lesparre, Jochem <Jochem.Lesparre at kadaster.nl>
wrote:

> 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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