The idea of the diversion is that you are making an unprepared amendment to your planned flight. The Examiner SHOULD say something like "We'll pretend that the weather ahead is deteriorating unexpectedly. When you are ready, I'd like you to divert to XXXX" If you don't know where XXXX is, then ask him/her to show you on your map (I always choose an aerodrome, hand the candidate the appropriate page from Pooley's and show him/her where it is on the map). Fly to an obvious feature which you can recognise, draw a line from there to XXXX on your map and do your in-flight re-planning. Then set off, but update your progress with some map-reading; we know that your in-flight estimation won't be as accurate as your pre-flight planning and that you'll need more frequent visual fixes to assist you. Always remember that THE EXAMINER WANTS YOU TO PASS!! The idea is that you can SAFELY divert if the local weather-wizzard has cocked-up his forecast.