What Spatial Reference System do I store Google Map's Lat/Lng in

Question

I am new to PostGIS, Spatial Reference Systems and projections and want to store lat/lng coordinates retrieved from Google Maps and Openstreetmap and its services like the Geocoder/Nominatim. I'm working with data in America and the main calculations are for nearest neighbors. Results will be plotted back on a web map (eg: via Google maps API or leaflet)

Question: What spatial reference system is Google map using? I figured out so far that its the WGS 84 datum with the Mercator projection in the geographic coordinate system. Should I store the location data as it is, or transform to US National Atlas Equal Area EPSG:2163?

Since I will be calculating distances and finding nearest neighbors, if I guess correctly that doing nearest neighbor search requires transforming the entire table to EPSG:2163, then will the solution be to store the data in both Mercator and EPGS:2163?

Answer 1

Google uses epsg:3857 crs, sometimes known as epsg:900913. I think your strategy for storing coordinates in both systems is okay, however, you could also store the in epsg 4326 with a geography data type, this would give you precise measurements with latlng coordinates (thats the reason behind geography data type compared to geometry data type)

Answer 2

While the Google map is displayed in Web Mercator (EPSG:3857), when you want to plot things on it, you would use geographical coordinates (and google will automatically convert that to display correctly on their web mercator maps). https://developers.google.com/maps/documentation/javascript/reference#LatLng

Thus, I'd recommend storing them in EPSG:4326 (and not in web mercator).

Whether or not you should also store them in EPSG:2163 depends on how you are doing your nearest neighbor calculations.