I have been meaning to post this for sometime but as I am local I know the trap.

The boundary separating CTA D in the south sector of Birmingham airspace between 1500' and 2500' feet is far from clear. On the VFR charts there is a clear blue dashed line, but not on Skydemon, see attached. The line runs diagonally from North of Henley in Arden to Snitterfield.

Travelling east to west or west to east it's not at all clear that the ceiling changes. the line is there in faint blue if you really zoom in but sooner or later someone will get caught out,

thanks.