GeoLength

GeoLength[g] gives the length of the geo path g.

Examples

GeoLength[GeoPath[{Entity["City", {"NewYork", "NewYork", "UnitedStates"}], 
  Entity["City", {"London", "GreaterLondon", "UnitedKingdom"}]}]]

GeoLength[GeoBoundary[Entity["Country", "France"]]]

Please visit the official Wolfram Language Reference for more details.