You may already read the articles on WGS 84 Web Mercator / WGS84 Web Mercator (Auxiliary Sphere) and WGS 84 (ellipsoid). For example,
- The Google Maps / Bing Maps Spherical Mercator Projection | Alastair Aitchison
In practice, how do you deal with the datum/projection transformation between WGS 84 Web Mercator / WGS84 Web Sphere Mercator and WGS 84 (ellipsoid). Also, how to transfer major local datum /projection like WKID 102204 (Ain_el_Abd_1970_Aramco_Lambert_2 ) into WGS 84 Web Mercator / WGS84 Web Sphere Mercator 'properly'?