Web Mercator Projection Web Mercator, Google Web Mercator, Spherical Mercator, WGS 84 Web Mercator or WGS 84/Pseudo-Mercator is a variant of the Mercator projection and is the de facto standard for Web mapping applications. It rose to prominence when used in the first Google Maps in 2005. ChartTiff offers Topographic maps, NED and DEM Elevation Data and NAIP and USGS Aerial Images in Web Mercator. Wikipedia has an on-line description of this projection at:                                           https://en.wikipedia.org/wiki/Web_Mercator WEB Mercator Projection uses EPSG:3857. For GeoTIFF formats, the GeoTIFF record PCSCitationGeoKey  contains the following string for ESRI applications:    ESRI PE String = PROJCS["WGS_1984_Web_Mercator_Auxiliary_Sphere",    GEOGCS["GCS_WGS_1984",    DATUM["D_WGS_1984",    SPHEROID["WGS_1984",6378137,298.257223560493]],    PRIMEM["Greenwich",0],    UNIT["Degree",0.017453292519943295]],    PROJECTION["Mercator"]    PARAMETER["central_meridian",0],    PARAMETER["standard_parallel_1",0],    PARAMETER["false_easting",0],    PARAMETER["false_northing",0],    PARAMETER["Auxiliary_Sphere_Type",0],    UNIT["Meter",1]]    which is a copy of the .prj file created by ChartTiff for each file of WEB Mercator Projection. For GeoTIFF formats, the GeoTIFF record GTCitationGeoKey contains the following string:    PCS Name = WGS_1984_Web_Mercator_Auxiliary_Sphere Some Elevation data file formats do not support WEB Mercator Projection, including:    USGS DEM    PLS-CADD XYZ File Format    C Tech File Format