Create a "Spatial Data Formats" reference page

Richard Loveland (rmloveland) commented:

We will need to define what spatial data formats we support. This is needed for linking across function docs, etc.

Supported types for 20.2:

- WKT, EWKT
- WKB, EWKB
- GEOJSON

Estimated work:

- Create a 'Spatial Data Types' page
- On that page, each of the above gets a heading with a description of what it is, and what supported functions operate on it. Also any gotchas (if any)
- ... etc

Jira Issue: DOC-621