So here's an odd fact for you. It's possible to be less than a mile away from Downtown Manhattan, and yet not be in New York City at all. Across the River Hudson, just moments from the financial district, you’ll find the independent city of Hoboken, New Jersey.

What's even better, for those who fancy saving a cool 30 per cent on their rent, it's served by its very own 24-hour metro: the Port Authority Trans-Hudson (PATH) subway system, which links Manhattan with the suburbs just across the river. The system means that stretches of New Jersey suburbia are more convenient for the heart of Manhattan than anywhere you’ll find in Brooklyn.

And yet, even many New Yorkers are only vaguely aware that it exists.

The 13-station PATH network first opened in 1908, just four years after the first subway line in New York proper. It shares five stations with the Metropolitan Transit Authority (MTA) subway system; crosses the Hudson through two tunnels (one from the Village, the other from the Battery); and provides frequent services to Hoboken, Jersey City and Newark.

There are no free transfers between the two networks; but both are compatible with the Metro Card ticketing system. The PATH is as much a part of New York’s transport system as the DLR in London, or the S-Bahn in Berlin.

And yet, the city's standard subway map does its best to play down the existence of New York's second rapid transit network, showing it in the same thin blue line it uses for infrequent heavy rail services. What's even weirder is that it's entirely silent on the existence of the state of New Jersey. Look:

An extract from the current MTA subway map. Note the lack of New Jersey.

So why has the MTA decided to exclude the PATH system? There's no rational reason for it from the perspective of the consumer, argues writer and digital media expert Stewart Mader. It's merely that, due to an accident of history, they've ended up run by different organisations.

This, Mader decided, is a bit silly. He lives in Hoboken, and works in Lower Manhattan, all of 12 minutes away on the train. And yet, "if you look at the map, you'd think there's nothing to the west of New York”.

And so, he's launched a campaign to get the MTA to start including the PATH on its subway map. It'd look something like this:

Click to expand.

By making the map himself, Mader told us, he hoped to demonstrate to the MTA quite how easy it would be to actually, well, make this map.

This is not a new idea. As late as the 1960s, the PATH trains did appear on the subway map, albeit in a different colour to the main system:

An extract of the 1968 New York subway map.

Resurrecting this combined effort could be an easy win for the city authorities, Mader argues, expanding the functional area of the city for many residents at almost no cost. "We live in an era when capital construction is expensive. But ‘expansion’ doesn't have to mean building a new line – it can come from giving a clearer map."

Mader's campaign has attracted support from the mayors of Hoboken and Jersey City (well they would, wouldn’t they). Those who'd have to make the final decision, though, are the authorities at the MTA itself. Watch this space.

You can read more about this campaign here.