There's been talk on the Fedi about why online maps like OSM and Google use the Mercator projection, and I think it needs a bit of clarification. (Do NOT snitch tag.)
Online maps are _mostly_ used at small scales, of a district or a city. At these scales, the earth is approximately flat, so users expect a map that is _conformal_, one that preserves angles and shapes.
Online maps are continuously zoomable from continents down to your house. They usually aren't rendered on your browser straight from vectors, but are batch-rendered offline into square tile images. If you're on a slowish Internet connection, you can see them loading individually.
As you zoom an online map, tiles get replaced with higher-resolution ones, and as you scroll, tiles get filled in to fill the gaps. You could theoretically scroll and zoom forever, so the map needs to not have a magically special reference latitude or longitude. These constrains mean that the map needs to be _equatorial_, so that no point gets special treatment, and _cylindrical_, so that meridians are vertical and lines of latitude are horizontal.
And which is the map projection that is all of equatorial, cylindrical and conformal? Mercator!
#Maps #Cartography #OpenStreetMap