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On the numbering of bus routes

Edinburgh is a city with a pretty good bus network. And if you mention this to almost anyone who lives here, they are likely to go off on a rant about how incredibly stupid it is that they are currently digging up half the streets in the city to put down tram lines. Apparently, according to several taxi drivers who have talked at me about the trams, it's one of the best bus networks in the world. Or maybe it was Europe. It doesn't really matter to our topic today, which is not going to be the trams, but rather prime numbers.

From time to time, I take the bus down to Leith, an area of Edinburgh were several of our friends live. As I get to my bus stop, I will usually have a look to see which routes that stop at that particular stop, and then I will check the route map in the bus shelter to see which of those buses go to Leith. And as it happens, the buses that go to Leith from my bus stop is precisely those whose route numbers are divisible by 7. For a while, I thought that perhaps this was a general rule, that all buses divisible by 7 go to Leith, but this turned out not to be the case. For example, the 22 goes to Leith, whereas the 42 doesn't.

Still, this got me thinking, and I had soon devised a clever system for numbering buses. First, you divide your city into areas, and then you assign each area a prime number. And then, in order to figure out the route number of a bus, just multiply together the numbers of each area it goes through. If we had used this system, and Leith had the number 7, then you would be able to tell at a glance that the 79534 goes through Leith, wereas the 34086 doesn't. Pretty clever, if I might say so myself.

-Tor Nordam


Mary,  10.07.10 22:16

Now, I do agree with you in principle. However, most people won't have the necessary maths skills to be able to tell at a glance that 79534 goes through Leith. I think, perhaps, a better idea would be to concatenate the numbers of the areas it goes through, rather than multiply. So, if Leith was 7, New Town was 5, and old town was 3, you could have a bus number containing 753 (or 357), etc.

Tor,  10.07.10 22:20

Ah, but that would only work for cities with 10 areas. However, as I realised while writing this article, one could use the letters, thus getting up to 26 (or 29, in sensible countries) areas.

Mary,  10.07.10 22:22

Hm, I suppose that is a point. It is a tricky question. I do, however, stand by my point that general people (Leithers especially :p) wouldn't be able to do the division to check if a bus went somewhere. :p

Tor,  10.07.10 22:24

Everyone could start wearing those watches with a tiny calculator on.

Mary,  10.07.10 22:31

Fair point. That is the perfect solution. :D

Anders K.,  10.07.10 23:10

The simplest solution for everyone would be to write the destination in plain language on the front and sides of the tram or bus. Oh, wait. They already do! So there are actually people who pay any attention those numbers next to that?

Camilla,  11.07.10 14:47

It wouldn't have to get too big, would it? Not if you limited it to the area where it starts, the middle area and the end. 7 x 5 x 3 is only 105.

Tor,  11.07.10 15:05

Ah, but the idea was to fit in more information. The buses in Edinburgh already list names of three of the areas they pass on the front.

Anders K.,  11.07.10 22:32

I still think the efford of learning a complex numeral system would be the same as (and for dyscalculics like me far more than) just looking at or even remembering the route map. Then again, I guess there are also lots of dyslectics or "dysmappists" out there, so several parallel systems is not nessecarily a bad thing. How about painting each bus in a different colour?
Tor,  11.07.10 22:39

Anders, min gode mann. Lenge siden vi har sett en artikkel fra deg nå. Jeg må si jeg føler savnet. Noen sjanse for at jeg kan overtale deg til å skrive en?

Anders K.,  12.07.10 07:45

Ja, jeg har jo nettopp avsluttet min tilværelse som skoleelev, en tilværelse som i høy grad oppmuntrer til å gjøre allting halvhjertet og ingenting ordentlig. Så kanskje jeg burde sette meg ned og skrive ferdig noen av de cirka tretti halvferdige artiklene jeg har liggende fra de siste årene.

Tor,  12.07.10 11:33

Så nå har du blitt bibliotek-kar?

Anders K.,  12.07.10 11:59

Jeg tror det. I kjent stil har HiO latt være å registrere en av mine eksamener fra i fjor, så på papiret mangler jeg ett fag. Men jeg er uansett i arbeid som faglært, i alle fall ut juli, så du kan godt kalle meg bibliotekar.

Camilla,  12.07.10 18:29

Det betyr at det begynner å haste å finne ut hva den fobien for bibliotekarer heter.
prime numbers
bus routes