Clarification on multiple bounding boxes in an extent

[cportele]

As part of the discussion in #168 we allowed multiple bboxes and time intervals as part of the extent information for a collection, but for Core we basically restricted it to a single bbox/interval. I have not seen any API or client that has used multiple bboxes/intervals so far.

In the discussions in Common (see opengeospatial/ogcapi-common#91) the issue was raised that any client that just looks at the first bbox/interval and uses that will be mislead.

The idea of the change in #168 was to make it extensible for future parts. If no implementation is known to have used the multiplicity yet (we would need to verify this), it might be a good idea to address the issue by clarifying that

• the first bbox/time interval always includes the complete spatial/temporal extent (e.g., all of the US);
• the second to nth bbox/time interval would be a more detailed extent specification (e.g., the bboxes of the continental US, Hawai, Alaska).

Clients that just want the simple solution (a single bbox/interval) can just use the first array, just as they do now. Clients that want to process the details can do that, too, with the additional clarification about the first bbox/interval.

Any thoughts?

[cportele]

Meeting 2021-03-15: We agree that this is a helpful clarification. We need to clarify that the second to nth bbox/time interval covers all features. And the first bbox/time interval is the union of the 2nd to nth bbox/time interval. @cportele to draft a PR and then we can ask implementers, if they have any concerns/issues with this.