ADR 0033 — A measurement borrows its sample’s location only for a viewer who may open the sample

Status: accepted

Decision

A measurement with no location of its own is treated as being where its sample was taken, but only for a viewer who may open that sample. For anyone else it has no location. This effective location is written once, in Measurement.objects.with_effective_location(user), and the measurement page, the measurement lookups, the collection tables and a dataset’s spatial coverage all read it.

The REST API returns only a measurement’s own location, never its sample’s.

Why

Most measurements are made where their sample was taken, so asking for the same coordinates on every measurement would be repetition. A measurement can belong to a different dataset from its sample, though, so it can be public while the sample is not. Without the check, a visitor could read where an unpublished sample was taken from a public measurement, or work it out from which area searches return the measurement.

Writing the rule in one annotation keeps every surface agreeing about what a viewer may see.

The API leaves the fallback out because a measurement’s response would otherwise change when its sample changed, with nothing in the response to say so, and every serializer would need the viewer’s rule. A script that wants the sample’s location follows the sample link.

Consequences

• Searching measurements by place, and the spatial coverage of a dataset, give different answers to different viewers.

• Anything built later on measurement locations, such as maps or area tagging, reads the effective location for the viewer rather than the sample’s field.