Postcodes can be pretty straightforward, until they are not. The central part of the city is usually numbered 1, for example central Manchester locations like Manchester Piccadilly and much of the Northern Quarter are under the M1 postcode.

However, Manchester Town Hall's post code is M60 2LA while Manchester Central Library which is literally next door has a post code of M2 5PD.

The postcode system was originally developed by the Royal Mail between 1959 and 1974 to enhance and streamline postal delivery.

Before then there was a much simpler 'postal district' system which was first introduced in London and then implemented in larger cities across the country including Manchester and Salford in 1867/68. The area was divided up into eight numbered districts.

So, how do postcodes work?

A postcode is a group of between 5 and 7 letters and numbers that identify a group of houses or addresses. The Postcode has two parts, an Outward and Inward code, separated by a space.

Each full Postcode contains around 15 delivery points and each postal delivery takes place in two stages. When a letter is collected it is routed to a main sorting office identified within the first part of the Postcode, the Outward Code (EG: M5). The local sorting office uses the second part of the Postcode, the Inward Code, to direct a letter right down to the individual Postman’s walk.

A postcode area or the outward code , EG M15 or M9 is the area that your local Delivery Office delivers to . In most of these cases if you live in M15 for example, the same postcode area would be any other postcode commencing M15.

The second part, or the inward code is used to sort the mail INTO the local area delivery office. This part is one number followed by two letters. The number identifies the sector in the postal district. The letters then define one or more properties in that sector.

What are the postcode sectors?

Area postcodes - Level 1

EG: M or SK

The country is divided into 124 Areas denoted by the first two letters of the Outward half of the Postcode. The average number of delivery points within each Area is 183,000.

District postcodes - Level 2

EG: M30 or SK4

Each Area is subdivided into District Postcodes. The District is denoted by the number or numbers that complete the first half of the Postcode (or Outward Code). There are just over 2,900 Postcode Districts, an average of 21 Districts within each Area, and the average number of delivery points within each District is 8,200.

Manchester has 48 postcode districts from M1 - M99. Of course, there are some number missing, for example there is no M 91-98.

Some postcode districts cover multiple areas, M16 covers Firswood, Old Trafford, Whalley Range and Moss Side while M90 is exclusively Manchester Airport.

Sector postcodes - Level 3

EG: M15 4

Each District is further segmented down into Sectors (9,000 in total) which are denoted by the first number of the second part of the Postcode. This half of the Postcode is called the Inward Code.

Unit postcodes - Level 4

EG: M23 1WJ

The fourth and final level of the Postcode pinpoints a group of houses or addresses. Some organisations are allocated a unique Postcode to ensure the segregation of large deliveries of mail to a single address (Manchester Airport). There are other 31,000 of these in Greater Manchester.

(Image: Skyoptics Ltd)

Why do we use an alpha-numeric system?

For a few reasons - one of them is because the combination of letters and numbers means we won't run out of postcodes anytime soon. The current alpha-numeric system has enough potential combinations to create 48million postcodes.

The combination of letters and numbers was also chosen because people can remember a mixture of numbers and letters more easily than a list of numbers. For example, you are likely more familiar with your postcode than you are your bank account number or your sort code.

Why is the alpha-numeric system not in a specific order?

Going back to the previous point about the city centre and surrounding areas having wildly contrasting areas, or even the areas around Heaton Park having M8 and M9 postcodes and then an M25 postcode seemingly out of nowhere, there are a couple of reasons for this.

The Royal Mail explained that "Postcodes were created for the original routing of mail and as such may not reflect the exact geography of an area."

Obviously Manchester was not all built at the same time so as the area expands in multiple different directions it's impossible for all the post codes to match up in an aesthetically pleasing way.

"Postcodes that run in numerical sequence were created around the same time," Sophie Dent, Communications Executive at Royal Mail explained.

"Postcodes that do not fit in with this sequence relate to sectors that were built up at a later date. There was also a recode in the Salford area in 2002 which is why some of the codes in this area seem out of sequence."

Certain postcodes that imply to a minute area or sometimes just one singular building are usually linked to a PO Box rather than a postcode district.