lonLatAt

Inverse of tileAt: the geographic point at a fractional position within tile — localX/localY in the tile's own [0,1]×[0,1] unit square, the same convention ContourPoint uses. Needed to place contour geometry (which ContourGenerator emits tile-local) on a real map; nothing here needed the inverse before.

Standard inverse spherical Web Mercator — the mirror of tileAt's own asinh(tan(...)) forward transform.