Mapping legacy/source system codes to FHIR

Looking for some advice regarding acceptable approaches to mapping coarse concepts within a source/legacy system to more granular valuesets defined within FHIR.

This is not an uncommon problem in many systems and not necessarily a FHIR issue, but Im looking to see if FHIR community has any specific suggestions/guides to address this issue.

thanks much

It very much depends on the type of the value set, and the element using it. can you provide some specific examples?

An example would be route of immunization admissions. Consider the following


The referenced FHIR codeset for this concept is more granular


well, the 5 concepts you named in the MIIS list all have direct equivalents in the v3 immunization list so you could just use them directly.

However note that this is list is not used directly. The immunization resource has an example mapping to a subset of the codes from this list. The point of it being an example mapping is that you can use what ever codes you like in this place - that list is just an example to show you what kind of codes you could use