A map is an association between codes from one code system and codes from another code system, that have the same (or similar) meaning. Mapping is the process of defining a set of maps. Maps are developed in accordance with a documented rationale, for a given purpose. As a result, there may be different maps between the same pair of concepts or terms to meet different use cases.
The purpose of mapping between SNOMED CT and another code system is to provide a link between the code systems, to obtain a number of benefits. These may include:
- Data reuse - for example, SNOMED CT based clinical data can be reused to report statistical and management information using an alternative classification system
- Retaining the value of existing data when migrating to newer database formats and code systems
- Avoiding the need to enter data multiple times and preventing the associated cost and potential errors
- Promoting interoperability between terminologies, classifications and code systems
Table 3.1.5-1: Requirements for a set of maps between SNOMED CT and another code system
| Requirement | Description | Example Use | Reference Set |
|---|---|---|---|
An equivalence map | A set of one-to-one bidirectional maps between SNOMED CT components and codes from another code system | Mapping legacy codes to equivalent SNOMED CT concepts | Simple map reference set |
A non-equivalence map | A set of maps from SNOMED CT concepts to codes in another code system, where the map may include:
| Representing a map from SNOMED CT to a statistical classification | Complex and extended map reference sets |
A set of maps from another code system to SNOMED CT,
where the map may include:
| Representing a map from a statistical classification to SNOMED CT | Complex and extended map reference sets | |
| A set of links between codes in another code system and SNOMED CT expressions | Representing the link between LOINC codes and SNOMED CT Expressions | Customized reference set |
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