D3 API used to map a geojson with cartesian coordinates (instead of lat-lon's). Uses an override of standard D3 geo projection behaviour: don't perform a full projection and resampling, but only a 1st order (affine) translation and scaling to transform real-world XY-coordinates into SVG screen coordinates...

map scale=scale px/mapunit; x offset=x offset px; y offset=y offset px;