discuss: enabling categories on all endpoints

Issue https://github.com/pelias/api/pull/1401 brought up the topic of whether we should enable the categories feature by default across all endpoints.

Currently, we have support for categories which goes back to 2015.
The feature consists of a single elasticsearch field with strings analyzed as keyword, so it's very simple but can also be very powerful for industry and interest-specific queries.

When we went to release the feature there was some concern internally at Mapzen about the default taxonomy labels I had selected and the WOF team was preparing an improved list, this work unfortunately never got finished and so the feature was left in an awkward state of half-release, available, yet also hidden from view.

Over the years we've had a bunch of issues and PRs opened regarding categories and the theme seems to be that organizations find them useful.

What would be required to completely release categories as a first-class feature?

• improved documentation including how to use custom category labels
• return categories by default in all geojson feature responses

Are there any concerns regarding the release of categories?

• once released any category labels become part of the public API, making them difficult to change or remove
• some organizations might prefer to opt-out of displaying categories, so it should really be optional?
• not all endpoints support categories, for instance: placeholder or PIP service results might not filter or display as expected

This ticket is open to discuss the pros/cons of enabling the categories feature by default and think through the work which would be required if we decided to go down that route.

cc/ @pelias/contributors

Start with PR #1401 and the Taxonomy-v1 wiki page, then review the linked categories issues and each endpoint's GeoJSON response behavior. Done would require an agreed decision on defaults, opt-out behavior, unsupported endpoints, and documentation scope; the issue does not identify implementation files or tests.