Why Postcodes Cannot Pinpoint Exact Locations

A postcode tells you which delivery area an address belongs to. It does not tell you which door, gate or building entrance is meant. That gap is built into how postcodes are designed, and it explains many failed deliveries.

Designed for sorting

Postcodes were created to route mail to delivery rounds, as described in the history of postal codes. For that job, a group of addresses is enough, since a carrier finishes the last stage using the street and number. Nobody needed a precise point.

What "area" really means

The size of the area varies. In cities a code can cover part of a street; in the countryside it can span a whole district. In both cases the code stands for a set of addresses, not a position. See how big is a postcode area.

Where this causes problems

• large sites with multiple entrances, such as campuses, hospitals and estates
• buildings with a main address on one road and a service entrance on another
• rural properties reached by long private tracks
• new developments that map services do not yet show
• areas with informal or missing street names

In each case a driver may arrive at a point near the code but not at the right entrance.

Postcodes in maps

A map service that accepts a postcode usually places a pin at a representative point for the whole area, not at your door. How that works is covered in can a postcode be converted to coordinates.

Closing the gap

The usual approach is to supply additional information: a house name, directions, a phone number or a map pin. A short exact-location code is a compact version of a map pin. UPCS represents a point as a code for a 3 m by 3 m cell, so someone can look it up and get coordinates and directions. It is optional, it is not an official postcode and it does not replace the normal address.

Read more in exact-location codes and postcodes together.