172, what datum was selected to cause an error that big?
Going back to the ground feature recognition business: I don't think the pilot is free to pick landmarks. He has to use whatever is on the CAA chart, and that doesn't show that much detail. Not even the 1:250k chart, which is better for dead reckoning than the 1:500k one.
I gather that specialised flyers, e.g. pipeline and power line inspection people, use the 1:50k Ordnance Survey charts. I don't know how they manage something like that in the cockpit, but one can run them on a GPS running Memory Map. However, such a chart is going to be very hard to use for normal flying.
So it's back to the CAA chart, or whatever chart you can get for some other country you are flying in, and what appears on that. One can't make use of a ground feature that doesn't appear on the chart. I don't think learning the local area is of much help; that's what instructors do by rarely venturing past the nearest crease in the chart but it won't work further afield.