A Mathematical Theory of License Plates | Hacker News Reader

A Mathematical Theory of License Plates

blog.charliemeyer.co

39 pointscsmeyer23 comments

I've always felt that besides all the jokes about German efficiency and precision, German license plates actually have lots of cool and helpful features:

They use a font intentionally designed to make simple alterations such as F->E harder and/or more obvious [0].

They aren't a random sequence of characters - they have semantics built-in: A German license plate follows the pattern

    [A-Z]{1,3} [A-Z]{1,2} [0-9]{1-4}

(my knowledge here might be a bit outdated)

where the first tuple is the issuing authority, the second tuple a qualifier thereof, and the third tuple just a random digit sequence.

The issuing authority is a variable-length optimality-based code: Large issuers like the state of Berlin get "B", whereas the city of Bitburg gets "BIT".

The qualifier follows the same idea: Plates issued in a rural area (AFAIK - I'm a bit rusty on the topic) generally have 1-letter combinations, while ones issued in cities have 2 letters (for a larger address space compared to adding a digit in the third tuple)

So what's the point? Well, motorists can immediately tell if another vehicle is

* from out of state (similar to the US - because all license plates have the state's signet on them)

* from out of town (so if you're in an urban area, they probably don't know their way around and you should keep some distance)

* from the deepest of rural areas (so not only will they not know their way around, they might also not know what a bicycle lane or a roundabout are, given the state of rural German infrastructure).

[0] https://en.wikipedia.org/wiki/FE-Schrift

Finland used to do the same. They gave up when they realized that requiring people to reregister their cars after moving was a huge, pointless hassle, plus the original scheme was starting to run out of number space, meaning that big issuers like Helsinki were already using multiple non-obvious letters.

You can nowadays keep your license plate in Germany when moving.

After decades of living in CA where plates stay with the car (unless vanity) I was floored to learn there are states where the plates stay with the person.

> They gave up when they realized that requiring people to reregister their cars after moving was a huge, pointless hassle [...]

I understand why this hasn't caught on here in Switzerland /j

And that somebody can see you are from out of town, is one of the things I dislike the most about German license plates...

Swiss here: I love it. Makes me understand why you drive like a newbe in my town.

German license plates also have one non-obvious pitfall: the space/dash between the two first letter groups is significant, which breaks various systems that normalize alphanumeric codes by removing spaces and dashes.

Quite a few countries in Europe have the issuing authority scheme (Serbia, for one -- but there's probably a list of countries which do this somewhere). While you could argue it is sometimes useful to know if a car is from out of town, it just helps form stereotypes (drivers from X are awful, etc).

> the third tuple just a random digit sequence.

Is it actually random? Most license plate issuers use sequential allocation for the portion of the plate not otherwise restricted by use, and I would expect Germany to as well (unless they're trying to avoid the German Tank Problem[1])

[1] https://en.m.wikipedia.org/wiki/German_tank_problem

Sorry, "arbitrary to the observer" :).

(I can hear my old distributed algorithms prof shouting at me even after years after graduating)

Here in Texas vanity plates can even get some limited symbols such as a heart shape. Makes for some interesting reading.

It’s expensive to maintain comparatively speaking, but I love my Office Space joke reference and once every 6 months somebody makes me roll down my window at a stoplight to ask if it really stands for “PC Load Letter” and when I confirm they laugh really hard.

I’ve got a habit of snapping pics of some clever or personal ones here in the DFW area. Maybe I should set up a sub stack or something.

I had one for a long time that wasn’t immediately obvious, but if you got it you got it: IMAYHOO

I later added a ‘Did you Yahoo!?’ license plate frame and more people seemed to get it (and not think phrases like ‘I may hoo?’).

I've had AFK for about 20 years as my vanity plates.

My next car which i get in a few months will get NIMHROD :-)

Nice! Years ago when I worked in downtown Dallas there was a really slick and loved Dodge Challenger with the plate “HAX0R” and I was impressed!

I always thought a vanity plate such as “0OQ1I” could easily evade the authorities.

And it would surely stress-test any operating ANPR system.

Makes me wonder if there is a calculable "annoyance" score for license plates.

I imagine single plates like that would already be defeated by calling in "Black Dodge, really annoying license plate that's all ones, Ls and Is"

Some vanity plate systems will let you get one of them (either CODF1SH or C0DFISH say) but once you get one nobody can get the other.

https://xkcd.com/1105/

This comic is what inspired me to start answering "security" questions with one word and five numbers, so my favorite musician is whimsy32910.

Filling a security question in with a hard password can be bypassed by "gosh, I didn't know you'd ever use those (because I'm smol and need help!), I just mashed the keyboard". A random word with a few numbers they'll check.

I use a randomly generated passphrase and store it in my password manager (like "correct horse battery staple" but usually 8 words).

You’d be much better off finding similar cars and copying their plates and using them when needed.

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