A little history and a little math
When we were looking at places to live in the UK our agent made an offhanded comment that he knew where almost every place was, down to the street, based on the just the postal code. Coming from the US where zip codes can cover up to 13,431 square miles (Zip code 99557 holds this record and covers about 701 people in Central Alaska) the ability to use a zip code to identify a specific street struck me as quite surprising.
A zip code in the UK is called a postcode and is a six to 8 character code. Unlike zip codes in the US, postcodes can include both letters and numbers. By using letters and numbers the UK is able to access a possible postcode set of 2,176,782,336 combinations (compared to the possible 1,000,000 combinations in the US using just numbers).
Postcodes, in their current format, are relatively new to the UK - formalized in the late 1950s. London postcodes are much older, going back to the early 1900s.
How to read a UK postcode
Postcodes in the UK are broken up into two parts. For this example, we'll use the the postcode NW3 6SG. This postcode happens to correspond with one of our favorite pubs, the Holly Bush (more on that, here).
NW3 6SG
These six letters actually tell you a lot about where the pub is located. The first three letters NW3 are the outward code. They are geographic and in this case, they tell you that it's in the northwestern part of London (NW). These outward codes are used to route mail to the right post office.
The second part of the postcode 6SG is called the inward code. This helps the local post office know where to route the mail. This gives each regional authority roughly 46,656 unique inward codes to choose from and as a result, they're very specific (usually down to the street).
If we type in the postcode to Google maps, this is what we see:
Why this is pretty neat
Not only does this system help the post office quickly route and sort mail, it also has some unique benefits in terms of user experience.
In America, when asked to enter your address on a website you'd have to type in the whole address.
However, thanks to the UK's postcode system, many websites will just ask for your postcode and immediately present you with a list of house numbers to choose from. Six characters and you're done. Pretty neat.
Postcodes are also far more informative than zip codes. Telling someone you live in NW3 or SW2 means something here. It helps people find you and in the case of our agent, helps you create a mental map of the city.
It took us a while to get used to the new postcode system, but now that we know how it works - it actually seems more efficient than the zipcode system of the US.
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