World War two
Not that this will be of any help to the OP but I recall something my old instructor said to me during a nav exercise in the mid-seventies which went something like this:
"You ought to be grateful that we had a world war a few decades ago" and naturally I asked him why, to which he replied "with all the active and disused airfields we have spread across the landscape, marking waypoints on your track couldn't be more simple". He had no problem spotting them due to the fact that he'd been an ATA pilot during the war and most probably visited more than the average RAF pilot had when delivering various types to airfields across the country from the factories.
Fifty years on with many of the disused airfields obliterated through residential/commercial development and agricultural activities there's not so many around that are readily discernible from above but back then they were a godsend.