Defining the map scope

SNOMED CT contains a number of hierarchies, each representing different types of concepts. When mapping to SNOMED CT, it's important to understand the scope of the source content that you are mapping so you can define the SNOMED CT scope appropriately. When mapping to SNOMED CT, you should constrain the target scope to a specific hierarchy, subhierarchy or subset of SNOMED CT. This will improve the accuracy of any automated mapping tools you may be using and also reduce the risk of errors from users developing the map.

Example scopes:

• If you are mapping a type of organ or body site, then the map scope might be the ‘Body structure’ hierarchy ( < 123037004|Body structure|)
  
• If you're mapping conditions, judgements or assessments about a patient, the scope might be the Clinical finding hierarchy ( < 404684003|Clinical findings|)
  

Mapping process

During the map process, once the target scope has been defined to the appropriate hierarchy, subhierarchy or subset of SNOMED CT, authors and reviewers can then search for an appropriate code to map to.

When selecting a code, the user must review the concept’s Fully Specified Name and defining relationships to understand the intended meaning of each concept, and use the use case and rules of the map (such as requirements for equivalence, allowance for 1:many maps, context of implementation, etc) to determine what is an appropriate match.

An example process a user may conduct is

• Search SNOMED CT for a matching concept
• Find an appropriate candidate concept
• Assign it to the source code with a relationship type

There may be instances that there is more than one candidate concept, depending on the rules of the map, it may be appropriate to select more than one. It may also be appropriate to select the most general supertype concept that completely matches the required semantics.

Where there are no appropriate SNOMED CT concepts available, it may be appropriate to

• Create or request an appropriate precoordinate concept in an extension to be used in the map
• Use a SNOMED CT postcoordinated expression that captures meets requirements if the use case of the map can support this
• Define the map as having no map target