Indeed though there are numerous cases where Zone 6 goes beyond Greater London:
- Thames Ditton and Hampton Court - which primarily serve an attraction within Greater London (Hampton Court) and presumably are deemed to have sufficient capacity to handle the ‘railheading’ that being in Zone 6 generates
- Stoneleigh, Ewell East and Ewell West
- Moor Park - albeit this is dual zoned with Zone 7
- Elstree & Borehamwood
- the eastern end of the Central line - here Zone 4 mostly goes to the boundary of Greater London, with Zone 6 stretching well into Essex. In fact, Roding Valley, Chigwell and Grange Hill are all in Essex yet are still in Zone 4!
- Whyteleaf, Upper Warlingham, Whyteleaf South and Caterham
- Chipstead, Kingswood, Tadworth and Tattenham Corner
- Banstead and Epsom Downs
The last Zone 4 station on a particular line varies from being as much as 11.9 miles from Charing Cross (Grange Hill) to as little as 7.8 miles (Meridian Water). Meanwhile the last Zone 6 station varies from as much as 16.6 miles (Harold Wood) to as little as 11 miles (Surbiton, in mainline or Guildford direction).
So as you say, there isn’t much geographical consistency - 11 miles from Charing Cross could equally put you in Essex yet in Zone 4 (Grange Hill), or in Greater London but in Zone 6 (Surbiton).
