Roland Perry wrote:
In message , at 23:13:27 on Fri, 8 Aug
2014, Tim Roll-Pickering remarked:
My theory then, which I'm beginning to think is too simplistic, would
require some kind of new coding to cope with any additional stations, and
it's odd that National Rail acceptance on all the lines other than the
ones above stops dead at exactly the edge of Z6, when some of the
currently proposed extensions would make a lot of sense (eg extending one
stop to Epsom).

In several cases Zone 6 was extended to take them in - in the case of the
Epsom & Ewell stations, the boundary used to be after Stonleigh, Cheam,
Belmont and I don't know on the Tattenham Corner line. I think it was 8
years ago now that the zone was extended to take in both Ewells plus the
stub ends of the Epsom Downs and Tatteham Corner branches. I don't know
about the stations on the last line but most of the two Ewells, Banstead and
Epsom Downs are virtually unstaffed stations and I suspect part of the
rationale was that zones and, eventually, Oyster would increase the income.

That's right, and extending Z6 to Oysterise a station doesn't involve
having to add extra 'pseudo-zones' (such as Brentwood/Broxbourne and Shenfield).

And for places like Dartford the choice would be extending Z6 there,
making it Z7, or creating a brand new 'pseudo-zone'.

Isn't it that already, given that the normally z1-6 limited Freedom passes
are valid there, but zone-6 travelcards aren't.