-I have 2 active worldbuilding projects, Verdun, which is high fantasy, and Achetamor, which is urban fantasy. The following is part of Achetamor.

Constructed be the great wizards of past, veiled spaces are areas between touching points, a street between attached houses, a room between the wall and the wardrobe.

To access these spaces without becoming a wizard, you must locate it's entranceway, called an "archgate". Every archgate is different, you'll know it when you see it. It can be inside or outside, but typically appears as a bricked off arch or doorway.

The true sign of an archgate is the gatekeeper, every archgate has a gatekeeper. It could be a painting, a statue, a person, or anything else with a face. The most common is a face carved into the keystone of the archway. The gatekeeper cannot leave their archgate.

Speak to the gatekeeper, and if you believe with enough confidence that they are a gatekeeper, they will speak back, and may open the archgate and allow you entry.

Maintaining a veiled space is a constant effort, a wizard dedicates their life to preventing it's collapse, and is often the authority who tends to any issues it's residents may have, as well as greeting new residents where applicable.

It is a task passed down through generations. Very long generations considering wizards' lifespans.

Trap streets, named after the cartographic feature that often secretly discloses their location, are hubs for the aware to talk, hang out, trade, and often seek shelter, where they need not worry about accidentally revealing magic to the unaware. This is especially vital for those who have been visibly affected by magic.

In the event that a veiled space is unmaintained, or one of it's boundaries is broken through, there are two ways it can collapse: A Crumple, in which the boundaries moving inwards push the contents further inwards, crushing them into a single point, or: An Expulsion, where the boundaries moving inwards push the contents outward, pulling apart the touching spaces on the outside to make room for the new space between.

Putting aside the drama and tragedy of “Face the Raven,” a cool aspect of the episode is Sarah Dollard based it on a real concept - the “trap street”, a fake street mapmakers would put into a map to catch out copyright infringement. As someone who has always been fascinated by maps, I love the idea.

Imagine my surprise and amusement to discover an apparent trap street in a modern day city map! I was looking at a street atlas for cities and towns in Southern Alberta, and I was checking out a street map of the city of Drumheller (about 150 km northeast of Calgary) to check out an address, and something caught my eye. It was a street with a name that made me chuckle - Bowling Alley.

I’ve seen tongue in cheek street names before, so I went onto Google Street View to see if I could take a peek at “Bowling Alley”. If there’s a street sign or something I might take a picture or something next time I drive through Drumheller which I do several times a year. Before doing so, I checked the street index at the back of the atlas in case it might have been, you know, an actual bowling alley mislabled on the map. I’ve seen that too. I’ve see schools and churches plotted in the middle of rivers and lakes. But no, it was listed as a street. So go to Street View.

Bowling Alley doesn’t exist! Where the street supposedly runs, there’s a house and a yard. And the house on Street View appears to be 1960s vintage, it’s been around for a while. So this isn’t a new community we’re talking about, and Bowling Alley is a very minor street on the map - it’s not some new road extension they haven’t built yet. So I think it is a trap street!

A short piece, detailing the phenomenon known as trap streets. (Lyrics are from Magic, by Mystery Skulls.)

In the olden days, i.e. the 1990s, there was a practice among mapmakers to intentionally include trap streets on reference maps to protect the copyrighted material. The idea to fabricate a street, or the name, or a feature, implant a pattern... ideally something small enough that it won't mislead a map user or be noticed at all until the point where it is necessary to prove that someone else copied your proprietary data into your map. They are tricky to use in US court cases ever since a federal court ruled that, "the existence, or non-existence, of a road is a non-copyrightable fact."

Although they show up as artifacts in online maps, the practice seems archaic in the current era, where lines drawn on paper maps have been converted to digital file formats, usually though a painstaking manual process of georeferencing, tracing, and/or orthorectifying. Once geographic information becomes "data", the manual process of cleaning and maintaining it becomes an incidental rather than central part of map-making, a tedious and unrewarding process left to "data monkeys", "interns" and "quality assurance" teams. Trap streets seem romantic in the era of plain old errata which, once they have been integrated into a geographic data set, and copied, distributed, and reproduced, are near-impossible to completely eradicate.  Here is something I like to think of as a trap street, even though it is really an erratum: Sunset Reservoir!

Sunset Reservoir: Google Maps

Looks like an awesome natural space suitable for dog walking and sunbathing. Actually, it is an underground and completely enclosed... reservoir.

Sunset Reservoir: Google Maps & Google Street View

I think I know exactly where this error comes from, because when I used to work for the City/County of San Francisco, I used to warn colleagues about the "water bodies" shapefile that was passed around interdepartmentally -- in addition to Lake Merced and the lakes in Golden Gate Park, it contained this reservoir, most likely because it was originally created by the Department of Public Works to track the water resources of the city, not the locations of urban lakes. Should I press the "Report a Problem" button and let Google know?

They are in good company, I upgraded to Mavericks this weekend, so I can say definitively. It's also not fixed yet in Apple Maps:

And incidentally, here's an argument for manual data creation/curation. Open Street Map: