In the list of visit occurrences there is a type “laboratory visit” which, according to the definition is " Patient visiting dedicated institution, at a Care Site, within one day, for the purpose of a Measurement".
Does this mean that when a person comes to our hospital for a blood test I would map this as a laboratory visit?
And what if the person comes for an X-ray, (which is also a diagnostic procedure (or a graphic measurement if you like)) would I then map it as an outpatient visit, or would that also be a laboratory visit (semantically hard for me to adhere to 
)? Just curious as to the distinction between the two procedures.
Yes.
Which means it goes into the PROCEDURE_OCCURRENCE table. The visit is usually derived from the organization that did the x-ray, i.e. a hospital or ambulatory radiology clinic.
True. But usually our measurement are simple question-answer pairs with precise tests, not open ended “tell me what you find” type measurements. But we do have some to-do with the latter and how we capture the results.
I would map this to Outpatient laboratory visit, it has the synonym “Hospital -Laboratory Services provided to non-pt” since your description looks like an outpatient visit at the lab.