public DistanceMatrixApiRequest units(Unit unit) {
    return param("units", unit);
  }
Specifies the unit system to use when expressing distance as text. Distance Matrix results
contain text within distance fields to indicate the distance of the calculated route.

@param unit One of {@link Unit#METRIC} or {@link Unit#IMPERIAL}.
@see <a
    href="https://developers.google.com/maps/documentation/distance-matrix/intro#unit_systems">
    Unit systems in the Distance Matrix API</a>
@return Returns this {@code DistanceMatrixApiRequest} for call chaining.
src/main/java/com/google/maps/DistanceMatrixApiRequest.java