Explain Canadian postal codes to me

I get that Canadian postal codes increase alphabetically from east to west (A in Newfoundland, R in Manitoba, V in British Columbia, etc.). I get that the format is alpha-numeral-alpha-space-numeral-alpha-numeral. The first bit seems to identify a city; but the second bit seems to identify a specific address. Is the numeral-alpha-numera (second)l segment of Canadian postal codes analogous to the ‘plus four’ digits on U.S. ZIP codes?

A1B 2C3

A - Postal district. Typically a province makes up 1 district but Ontario and Quebec are sufficiently dense that they have multiple ones (M in Toronto, K is Ottawa, H in Montreal
A1B - Forward Sortation Area which encodes, where, type (rurual/urban) and section
2C3 - local delivery unit which could be a portion of a block, a delivery route etc.

So mine could be K1M 1M4. That means
Ottawa(K), Urban(1), Rockcliff Area(M), #10-22 (even) on Sussex Avenue (1M4).

Forgetting the answer, I’ve asked my Canuckian relatives this question more than once. Their invariable answer (canned, no doubt, for the benefit of iggerant southern cousins) is “one side of a street.”

Which is how we know that Santa Claus is a Montrealer – His postal code is H0H 0H0.

So it sounds like the second segment is more specific than a ZIP code, but less specific for a ‘ZIP+4’ code that identifies a particular residence. For example, I used to live in ZIP code 90034. My ZIP+4 for my particular apartment was 90034-49xx. The ZIP+4 for street address of the apartment building was 90034-49yy. The second segment of Canadian postal codes sounds like they might be like the -49yy segment of the ZIP+4 that identifies the building but not the unit. Is that close?

Postal codes were designed later than (basic) Zip Codes and learned from those mistakes. They left a lot of room for expansion. they also did letter-digit pattern because transposed pairs of digits seems to be the most common error with zip codes. 5 digits also did not allow for anything more specific than post office (hence the additional 4 digits later).

The final Postal code identifies a block (or two) one side of a street, i.e. a stretch of a postman’s route -they go down one side of the street instead of back and forth across.
then the postman had only to sort in numerical order within that small group. the sorting machines could sort by major group (IIRC the first 3 characters get you to a post office). Further mechanical sorting gets it down to the postman’s route, so he need only sort by two characters to sort his route.

However, larger buildings and high-volume customers get their own postal codes. Then their entire day’s mail can be mechanically sorted to one pile/bag.

The codes were arbitrarily assigned, unlike Britain where it seems to me they have existing districts and designators like NW( for North-West?) and multiple letters sometimes, not an alternating sequence.

So it was a guessing game - and they seem to have done well. They had to leave lots of room for growth; some cities, like Toronto’s suburbs, have expanded massively since the codes were originally assigned but I have not heard of any need to reassign codes…

But the second character is 0, which indicates a rural area. So I am forced to conclude that the North pole is a rural suburb of Montreal. :slight_smile:

Postcodes have been refined since the mid-nineteenth century; but the present longest-running system was implemented by the Germans in WWII. Britain started introducing modern postcodes in 1959.

Zip-Codes started in 1963.

That was the pre-post code system, the postal district system — it only hangs on in that people might add ‘NW’ or ‘SE’ on a letter to London; but is unnecessary: the postcode alone is enough with perhaps the house-number — British postcode are based on the nearest Post Town: the first two letters are. say, AB for Aberdeen, and diminish in area from there.

A British postcode would be in this form: AB15 8BY, which devolves down to maybe 5 - 10 houses.

I recall an interview with the Post Office spokesman in the early 1970’s after they devised the Canadian system; they specifically mentioned the transposition problem, and that the 5 digit US system was not precise enough (as the US had to remedy later).

The problem then with the UK is worse - there are only so many mnemonic codes with two letters. At a certain point you might get confusion, work around duplicates, etc. - plus the letter transposition issue in the last 3 characters?

(I spent 25 years mailing letters to relatives in Britain before I found out “nr” in the address meant “near”; someone mentioned that at a presentation once, and both a coworker and I said at the same time “Oh! That’s what that means!” We’d never realized it. )

I think the letter-digit pattern was purposely designed so that Canadians would have a harder time filling out forms on their smartphones a few decades later: switch to uppercase, type the first letter, switch the keyboard to numeric, type one digit, switch back to letters, switch to upper case, type the letter, type a space, switch the keyboard to numeric… :slight_smile:

A ZIP+4 doesn’t (necessarily) identify a particular residence. All three houses on my side of my street have the same +4.

Oh sure. Give them the letter that they can’t pronounce.

Probably hijacky, but I have a distant memory of a longer ZIP, ZIP+6 maybe, that was more specific, maybe to the house level. I think either it never got beyond planning, or else I made it up.


Just to clarify, you’ll see (for example) NW on a letter addressed to parts of London because that’s the form London postcodes take. For example, the postcode for the Houses of Parliament is SW1A 0AA. I presume this is because the city is so large that a single “LN” postal district would be unmanageable.

The British postcode system was, as mentioned above, layered over the existing postal district system that had previously been used,at first only in London, then copied in one or two other major cities, then gradually extended over the whole country in the late 20th c. London was originally divided up into arcs radiating from the centre (a number of alterations and amalgamations have taken place over the years). Until fairly recent years, nobody had much use for postcodes despite periodic appeals from the Post Office to use them, and it is still possible to get a letter delivered without one. If you went to the mail sorting office with a query and offered them a postcode even they said, ‘we can’t be bothered with deciphering those things’. But now no one will do business with you unless you have a postcode - it’s very difficult even to get utilities to deal with you if you can’t or won’t give them one.