The relationship between a landmark that helps determine a body location and the body location itself. The location relative to a landmark is specified by:

• Specifying the location and type of landmark using a body site code and optional laterality/orientation,
• Specifying the direction from the landmark to the body location, and
• Specifying the distance from the landmark to the body location.

The RelationToLandmark element is part of BodyLocation, a flexible structure that allows the location to be determined by a single code, or a code plus laterality and/or orientation. The body location can also be specified in relation to one or more body landmarks. SNOMED CT is used in all cases.

• Code only: The code should include (precoordinate) laterality and/orientation to the degree necessary to completely specify the body location.
• Code plus laterality and/or orientation: The basic code augmented by codes specifying the body side and/or anatomical orientation.
• Relation to landmark: The location relative to a landmark is specified by:

1. Establishing the location and type of landmark using a body site code and optional laterality/orientation, and
2. Specifying the direction and distance from the landmark to the body location.

Note that BodyLocation is a data type (a reusable structure), not a stand-alone entity. The concept is similar to how a postal address can apply to a person, location, or organization. This contrasts with FHIR's stand-alone BodySite (aka BodyStructure in r4) which 'is not ... intended for describing the type of anatomical location but rather a specific body site on a specific patient' (FHIR 3.5).

Unique id for the element within a resource (for internal references). This may be any string value that does not contain spaces.

May be used to represent additional information that is not part of the basic definition of the element. To make the use of extensions safe and manageable, there is a strict set of governance applied to the definition and use of extensions. Though any implementer can define an extension, there is a set of requirements that SHALL be met as part of the definition of the extension.

There can be no stigma associated with the use of extensions by any application, project, or standard - regardless of the institution or jurisdiction that uses or defines the extensions. The use of extensions is what allows the FHIR specification to retain a core level of simplicity for everyone.

The type of feature that constitutes the landmark, particularly if the landmark is an acquired body structure or physical object.

The body location of the landmark, specified by a location code and optional laterality and orientation.

The direction from the landmark to the body location of interest, given as a clockface direction or anatomical direction.

How far the body location of interest is from the given landmark.

Source of the definition for the extension code - a logical name or a URL.

The definition may point directly to a computable or human-readable definition of the extensibility codes, or it may be a logical URI as declared in some other specification. The definition SHALL be a URI for the Structure Definition defining the extension.

Value of extension - must be one of a constrained set of the data types (see Extensibility for a list).