Recently, the internet website CityMetric investigated Andrew Adonis’s claim that there was a strong case to move East & West Croydon up a TfL transport zone, from 5 to 4. It concluded that, based on distance from Charing Cross, there wasn’t an overwhelming reason to do so.

But, as noted in the original piece, measurements from Charing Cross might not be the best way to structure London’s transport zones. In fact, look at the map, and it clearly isn’t the measure Transport for London uses.

Here’s the actual geography of Zones 1-6. For the purposes of this exercise stations straddling two zones are considered to be in the lower, that is, the more central, of the two.

For a start, you can see that the zones are wider than they are long, so stations in the east or west tend to be in more central zones than stations a similar distance away in the north or south. This makes a certain amount of sense given that ‘central London’, as defined by Zone 1, isn’t a circle.

At any rate: the other zones clearly aren’t defined by their distance from Zone 1. Lewisham, which is in Zone 2 and 3, is the furthest Zone 2 station from any zone 1 station – 4.1 miles from the closest, Tower Gateway, as the crow flies. But Clapton station, in Zone 3, is only 2.2 miles from a Zone 1 station (Hoxton). What’s up with that?

More concerning than that is the totally ludicrous situation going on in the north east where Zone 4 appears to be trying to escape by eating its way through Zone 5 and a good chunk of Zone 6. And frankly, given that it’s Fairlop Loop, good luck and good riddance.

Out on the fringes of the network, the furthest Zone 6 station is Knockholt, a massive 14.2 miles away from Zone 1 – but Waltham Cross, only 10 miles outside Zone 1, is relegated to the weird outer zones.

(There is a sort of sensible reason for this one: Knockholt station, despite for arcane reasons being named after a village in Kent 3 miles away, is itself just inside the London border, whereas Waltham Cross is in Hertfordshire.)

So what should a geographically fair zone system look like?

Let’s assume that:

The current boundaries of Central London/Zone 1 are correct; The boundaries of the other zones should be formed by drawing a ‘buffer’ around zone 1 the distance of the current furthest station in the zone from its closest zone 1 station; Again, for stations in multiple zones only the most central has been considered.

Now, these are all potentially dubious assumptions (for a start, if we’re redrawing the zone boundaries there’s some stuff in Kensington & Chelsea that I think has a dubious claim to being ‘central’, when, say, Whitechapel is in Zone 2). But let’s go with them, assume this method of ‘Geographical Fairness’ is a good way to run a transport system, and redraw the map.

I’ve retained the colours of the station dots from the ‘real’ zone map so you can see broadly speaking see how this changes things: only small chunks like the one directly east of the centre roughly match up with the current state of affairs. All the zones have expanded; in some places stations that were in Zone 6 are in now in Zone 4.

If we take a closer look at south London, all three Croydon stations have been bumped up to Zone 4 status, as Lord Adonis believes they should.

Meanwhile, for Lord Elledge, Kingston has jumped two entire zones, joining Croydon in Zone 4 (which now stretches 9.2 miles from the centre of town, thanks to Grange Hill on the accursed Fairlop Loop.)

On the other hand, can we really stomach a London in which Chiswick is in Zone 2?

Here’s the full labelled map if you want to find out in which Zone your favourite station will end up if this new Geographical Distance fairness scheme is implemented due to some kind of error. Right click and open it in a new window to get a good look.