Maybe not for everything, and i'm sure there are loads of technicalities on the edge of london. But for your examples: EC1A and EC1M are both in or around the

Maybe not for everything, and i'm sure there are loads of technicalities on the edge of london. But for your examples: EC1A and EC1M are both in or around the city EN1 is enfield I think? So far north, EN10 I imagine is just further north KT9 I think is Kingston. Both KT9 and KT11 are probably south west near the edge of london > I can only manage that if you define London as "The area covered by the London compass-direction based postal districts" That's actually basically what I meant. Compass postcode = london, non-compass is effectively outside london (or on the very edge) Either way, the point that post codes carry a lot more information than codes generated from GPS coordinates still stands