Finding where the sun is…
At zero this returns the plain shortest route, which is what keeps the comparison honest. At three it will take a long detour for shade.
Shade is computed from OpenStreetMap building and tree shapes cast against the sun's real position at the time you pick. Park areas are assumed fully shaded and are reported separately, because only the first is geometry we measured. No temperature claim is made: shade cuts radiant heat, not air temperature.