Connectors on the Tube Map are so often the unsung heroes of London’s transport network. Because of its advanced age, many of the lines in the capital snake around each other and interchange in ways that a modern transport system built from scratch would never even consider.

This means some pairs of stations are linked to each other, either through physical connections (like the walkway between Hackney Central and Hackney Downs) or more notionally, via the street (like Forest Gate and Wanstead Park). These links often necessitate a ‘connector’ on the Tube Map, like the big one between Bank and Monument. However, the sheer number of situations in which these humble connectors are applied means they often fall victim to problems.

Case in point: Camden. TfL’s recent public consultation into its upgrade of Camden Town Station noted that the new station, moved up onto Buck Street, will ease interchange with Camden Road Overground station, an option opened up by the new station’s increased capacity.

Image: TfL/CityMetric.

This is already an official “out-of-station interchange” (OSI), which means you can change from one station to the other and have it count as one journey rather than the usual two, and so are charged less on Oyster. You can find the full list of those here.

What stands out, though, is that the interchange TfL is so eager to improve in Camden is one they currently don’t bother to tell passengers about: it just doesn’t appear as a connection on the Tube Map. Unless a savvy passenger were to check, they wouldn’t know that the two Camden stations are only a three minute walk apart.

This is particularly scandalous, given the relative rarity of viable Overground – Underground interchanges. Why would TfL purposefully mislead passengers like this? Moreover, how do they determine when to connect two stations on the map? This is a question that deserves answers, but it feels like there aren’t any.

There is literally no firm way of telling which stations deserve a connector and which don’t

Let’s start with a simple assertion: all of the stations that are connected by underground tunnels are connected on the Tube Map. This, obviously, holds up.

There are also above-ground interchanges, like Clapham High Street/Clapham North, which are signposted and don’t use tunnels. Even though travellers have to enter and exit a ticket gate to use these interchanges, they still work because there is an OSI between them.

But half of the above ground OSIs aren’t shown on the map. And Camden is just the first of many.

Why did they bother with these two but not those two? Image: Tfl/CityMetric

There are lots of stations with OSIs that don’t connect on the Tube Map

A relatively well known example of this is Seven Sisters/South Tottenham; there have been complaints in the past that, despite being just as close together as the two Walthamstow stations to the east, these two don’t appear connected on the map.

But that is simply the first in a line of peculiar choices. Take Dalston Junction to Dalston Kingsland: only a three minute walk apart, they don’t get a visible connection either, even though a sprint between these two could make the difference when catching a train that’s just left Canonbury.

There are even interchanges that really should have an OSI but don’t get one

There are two stations in London called Bethnal Green. The two are about an eight minute walk apart, but they don’t get an out-of-station interchange. You might be wondering whether this is really so egregious: after all, eight minutes is surely a long time, and passengers could simply stay on either line and change at Liverpool Street.

Well, if eight minutes is a long time, then the trek required for the official interchange between Euston and King’s Cross is even longer. As for the change at Liverpool Street, this is a fair criticism – but enabling passengers to change at Bethnal Green would mean they could change without entering Zone 1, and save money as a result.

Double standards. Image: Google Maps/CityMetric

But that sets a dangerous precedent, doesn’t it?

Maybe. If we give the OSI between Euston and King’s Cross a thumbs-up, why doesn’t it get a connector? What about the other Central London stations with OSIs? There’s actually quite a lot of them.

The OSI between Warren Street and Euston Square is one example. A simple three minute walk along Euston Road could shave a minute or two off a journey. However, it feels like putting a connector on the Tube Map here would be overkill: travellers could simply walk from Euston instead. Giving all OSIs connectors on the Tube Map could just mean needless clutter and senseless route planning.

And with that, we reach a peculiar sort of conclusion: according to common sense, some stations, like in Camden and Bethnal Green, really need connecting up – but that same common sense could make Central London a complete mess on the Tube Map.

Method in the madness, then?

Yes. So perhaps the fact that there are no hard and fast rules for connecting stations on the Tube Map actually results in a cleaner end result than if such rules did actually exist. It’s also a much safer solution than connecting stations willy-nilly.

That’s because connecting two stations up on a map completely changes how travellers actually behave. Connecting stations like Dalston and Bethnal Green seems good on paper – but do the same in Camden this evening, and by tomorrow you’ll have dangerous crushes in station corridors, because too many people are trying to get from one station to the other.

The same might happen if you connected Euston Square and Warren Street on the map: the junction between Euston Road and Gower Street is not designed for masses of pedestrians crossing east to west.

So, if the system for determining which stations to connect appears non-existent in theory, but relatively sturdy in practice, what remains to be said?

Well, for one thing, Bethnal Green and Bethnal Green. Sort it out, TfL. 

Want more of this stuff? Follow CityMetric on Twitter or Facebook.