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I am a bit confused on EPSG:4326 and EPSG:900913. I thought that they were both same. Though as I am placing my features over GMaps, which is EPSG:4326, I need to define the srsname of the WFS layer as EPSG:900913 to get it into the right place. If I define srsname as 4326 it is projected somewhere completely wrong.

Could someone explain it a bit more in detail as to what is wrong here?

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Yes, it does. The two are exactly equivalent. –  rudivonstaden Nov 20 '12 at 20:25
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To add to R.K.'s answer, EPSG:900913 uses an authalic sphere. –  arcsump Jan 24 '13 at 7:55
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As a point of trivia: 900913 was originally rejected as a credible projection by European Petroleum Survey Group (EPSG) so Google (who invented it for the web) gave it their own number, which if you type it on an old fashioned calculator spells 'googlE' (substitute '9' for 'g' and squint a bit). Eventually EPSG relented and allowed 900913 into its geodetic repository but gave it the number 3857. –  MappaGnosis Jan 24 '13 at 8:10
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@arcsump, 900913 (3857) does not use an authalic sphere. It uses a sphere with a radius equal to the semimajor axis of WGS 1984 ellipsoid. –  mkennedy Jan 24 '13 at 17:52
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@sylvester-sneekly, Google did not define 900913, Christopher Schmidt of OpenLayers did: crschmidt.net/blog/archives/243/google-projection-900913 –  mkennedy Jan 24 '13 at 17:54

2 Answers 2

up vote 26 down vote accepted

They are not the same. EPSG:4326 refers to WGS 84 whereas EPSG:900913 refers to WGS84 Web Mercator. EPSG:4326 treats the earth as an ellipsoid while EPSG:900913 treats it as a sphere. This affects calculations done based on treating the map as a flat plane which is why your features got plotted on the wrong places.

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Also, coordinate values will be totally different, EPSG:4326 has decimal degree values (-180 to 180 and -90 to 90) while EPSG:900913 has metric values (-20037508.34 to 20037508.34). –  Crischan Sep 26 '12 at 8:18
    
Ya i did notice how the co-ordinate values were changing. Thanks –  Sam007 Sep 26 '12 at 16:05

EPSG:4236 uses a lat/long coordinate system. Latitudes are = 90 - -90 and Longitudes are = 180 - -180

EPSG:900913 uses an x/y axis coordinate system.

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