WAYPOINTS

I created a waypoint. The .xml requires it to be associated with an airport and needs the airport ID, latitude, longitude, and altitude. I made a mistake and entered altitude in metres instead of feet. When I loaded a stored flight from the airport with the aircraft at the end of the runway, I found the aircraft hovering stationary several hundred feet above the airport at the height set in the waypoint .xml!This was easily corrected, but made me wonder that because approaches have also to be associated with a particular airport does this mean than only waypoints associated with that airport can be used in an approach?