There are two projection of maps that I saw online. UK CAA is a transverse projection map, while ICAO maps are conical.
It seems that transverse map is easier for flight planing as straight lines are rhumb lines, on the other hand the shortest route between two point is the great circle which is curved. So it's easy to calculate a heading, but it will not be the best route.
In conical map the straight lines are the Great circles so the best route, but its harder to calculate heading for flight.
What should be choosen and why? I didn't found info about this on the Internet...