CharlesPottins writes
Thanks. This seems not dissimilar to map that came with ticket. If it's
accurate, I'm dissappointed that Denham(Chiltern) is not included. But being
able to go to Amersham does seem a good deal.

Well Denham is outside Greater London.

There are a couple of places outside Z6 where you can go - on the Met
(coz it's a TfL service) and to places like Dartford. AIUI, the latter
easement is because hospital services for many residents of Bromley
Borough are in Dartford,

--
Dave