I'm trying to understand how WMS scale denominators translate to tile zoom levels. (Specifically, Google Maps zoom levels.) I found this answer to What ratio scales do Google Maps zoom levels correspond to? and this OpenStreetMap reference, which are in the same ballpark but differ by about 10%.
Why are they different?
Does it depend on the projection used?
Does it depend on latitude?
The width and height of the WMS request?
Note that I am not interested in true scales here. Given the min and max scale denominators from the WMS capabilities XML, and using using this approach to calculate the size and position of tiles, I want to know what zoom levels I can expect the WMS endpoint to provide images for.