House numbering is the system of giving a unique number to each building in a street or area, with the intention of making it easier to locate a particular building.
In Europe the most common house numbering scheme is to number each plot on one side of the road with ascending odd numbers, from 1, and those on the other with ascending even numbers, from 2, or sometimes 0. Where additional buildings are inserted, these are often suffixed a, b, etc. Where buildings are later combined, they may use just one of the original numbers, or give their address as a range (e.g. 13-15). Note that this range is of odd numbers only and does not include number 14. Where some plots are not built upon, there may be considerable gaps in the numbering scheme.
A less common scheme is to number all plots on one side of a street consecutively, then all plots on the other side with consecutive higher numbers.
In Venice, Italy houses are numbered by district, resulting in just six series for the entire city; in Florence houses are given black numbers and businesses red numbers, resulting in just two series.
Tokyo, Japan uses a system where the city is into small sections each with its own numeric code. The houses within that zone are then labelled based on the order in which they were constructed. This system is considered by many to be very inefficient.
In most of North America doors are numbered instead of houses. This is done according to municipal schemes which take into account the possibility of having several dozens of doors in a single block. As a result adresses usually have numbers in the thousands.
In some, usually remote areas, houses are not numbered at all, instead simply being named.