# World Stamp Catalogue/Numbering System

(описание на русском языке см. World Stamp Catalogue/Numbering System/Russian.)
A numbering system for a World Stamp Catalogue needs to be
* hierarchical - Each number begins with the most significant element, and ends with the least significant.
* scalable - There is ample room in the system to add new information, or to expand information on existing stamps.
* integrated - When required the system allows for co-ordination between countries and their subdivisions, occupiers and the countries they occupy, or common design issues.
* intelligible - Some brevity and conciseness may be sacrificed to make the code more understandable.

## Beginner level

Collecting and identifying stamps at this level should be easy, and should require no more equipment than a low-power magnifying glass. The different segments in this level of numbering may be separated by hyphens for easier reading.

### Countries

The most significant information about a stamp is the country where it was produced. This should thus be the first element in a catalogue number. It is strongly recommended that w:ISO 3166-1 alpha-3 be used as a basis for this. This could include historical codes for entities like the Soviet Union that no longer exist, but that previously included what are now separate countries.

### Political subdivisions

This optional entry may be used for political subdivisions that either produced their own stamps or had stamps produced for them. It may be left blank where no such subdivisions are catalogued. Cities which produced local stamps should be viewed as such entities. Although standard abbreviations are to be preferred these are not always available. When used, this entry should have two or more alphabetic characters.
It is conceivable that stamps with details in this position could be the basis of separate secondary listings that bring together all the stamps of the subdivision by themselve. At this time, in assigning subdivisional codes one should be mindful of potential naming conflicts with distant and unfamiliar parts of the world. To this end invented three-letter codes should be avoided.

### Year

The next element should be the year when the design was first adopted. The effect of this will be to bring everything produced with a given design together without regard to how long the design continued in use.

### Set and stamp segment

This is a four digit number which includes leading zeros informs us about the "set" of stamps, and the stamps within the set. A "set" refers to a number of stamps issued together, or having common design features. A set may include only one stamp, but sets with more than 100 stamps are also known. There are also a few instances where a country issued more than 100 sets in the same year. It is important to be able to adapt to varying circumstances without exceding four digits for this part of the number.

#### First and second digits

The first part of this number identifies the set. It may be advisable to segment this into general regular issues, commemorative issues, supplementary issues (like postage dues or postal tax stamps) and unlisted issues. One possible scheme for this could include
* 01 to 09 - regular issues, sometimes expanded over many years like the Machins of Great Britain.
* 11 to 19 - common designs or themes used by two or more countries at the same time; this will allow some degree of co-ordination.
* 21 to ?? - commemorative issues unique to the country; try here to conform to set issue date order.
When a country issued a very large number of sets in a year it may be necessary to combine sets for our purposes. The "n0" format in this position should be reserved for collective information.

#### Third and fourth digits

The second part identifies the stamps within the set, preferably in the order of their face values with allowance for stamps of the same value but obvious colour changes. Consecutive numbers may be used when one is reasonably convinced that no more new stamps will appear with this design. When this is uncertain the numbers should be spaced to allow for subsequent new issues. A "00" in this position should be reserved for collective material about the set.

## Intermediate level

At the intermediate level the catalogue user should be able to identify most of the major varieties found in the existing standard catalogues. This includes varieties based on overprints, colour variations, perforation, watermarks, paper varieties, printing type and others. It can also include information for identifying common forgeries and reprints.
This section has a hyphen followed by four numeric digits including any leading zeros. This could easily allow for four separate bases for variation. No constant order is specified for these variations, but it is strongly recommended that precedence should be given to the most easily identified variations.

## Advanced level

An additional final section of indeterminate length may be added at the end of a number. While it is recommended that this part of the number be organized with some logical basis in mind, the endless possibilities presented here prevent specific recommendations. This is the place to expand on such topics as errors and plate varieties.