EPSG:3857 is a Spherical Mercator projection coordinate system popularized by web services such as Google and later OpenStreetMap.
- OSGEO:41001 - OSGeo created this code while developing the Tile Map Service (TMS) specification.  It was superseded by 900913. (equivalent, deprecated)
- 900913 - Sometimes described as EPSG:900913, this was created for OpenLayers (equivalent)
- ESRI:102113 - First used by ESRI, but then replaced by 102100 (equivalent, deprecated)
- ESRI:102100 - Built differently, but equivalent to 102113 (equivalent, deprecated)
- EPSG:3785 - EPSG added this, similiar to how ESRI:102113 is defined (equivalent, deprecated)
- EPSG:3587 - was never a real EPSG code, but some used this likely as a mistype of EPSG:3785 (typo)
- EPSG:3857 - Equivalent to the depreciated code EPSG:3785. ESRI replaced ESRI:102100 with this (current) [CONFUSING - is ESRI 102100 the new or deprecated code??]
- 2007/08/06 - Christopher Schmidt of OpenLayers announces use of the number 900913 to describe the "Google Projection" 
- 2007/09/11 - Christopher Schmidt checks in OpenLayers/Layer/SphericalMercator.js with WKID 900913 
- 2003/06/25 (or earlier) - Google (or a user) begins using WKID 54004, either as EPSG:54004 or ESRI:54004 
- 2008/05/?? - EPSG updates mailing list that EPSG:3785 will be added to version 6.15 
- 2009/02/09 - EPSG changed EPSG:3785 to EPSG:3857 
- 2008/08/05 - Google Support thread on the use of Web Mercator in which it's noted (less technically) that the projection formerly used by Google Maps did not preserve azimuth at high latitudes.
- ?? - ESRI ArcGIS 10 changed the WKID for this projection from ESRI:102100 to EPSG:3857 
- 2010/09/15 - Noel Zinn from Hydrometrics gave a presentation at GIS in the Rockies on the mathematical uncertainty introduced by Web Mercator
- Official entry on EPSG Registry
- SpatialReference.org entry, however not as official EPSG code but SR-ORG:6864
- ArcGIS forum discussion on ESRI code history
- ArcGIS forum discussion on the two ESRI codes
- Tiles à la Google Maps: Coordinates, Tile Bounds and Projection - good discussion, including Python code to convert between lat/lon, tiles, pixels, and coordinates (in meters, EPSG:3857)
Warning: Default sort key "EPSG:3857" overrides earlier default sort key "3857".