Coordinates is defined as std::array<Coordinate, 2>, which does not inform on the order of the coordinate pair. Is it (Lat, Lon) or (Lon, Lat)? At first I made a mistake and provided the coordinates in incorrect order.

The situation could be improved by adding e.g. an enum: enum { LON_INDEX = 0, LAT_INDEX = 1};, or better yet, by defining coordinates as a struct with named members.