For users of Memory Map software, I?ve produced a calibrated map showing the Explorer map numbers and boundaries as a grid overlaid on a 1:1,000,000 scale map of mainland UK. It enables you to see at a glance which Explorer maps cover a particular area, or which ones are needed for a long distance route:- you just plot the route then switch to this geo-referenced grid map and read them off.

My
blog entry contains a bit more technical detail and a link to the Contact page for anyone who would like to download it.