We need a spatial index for spatial (columnar) data!

- https://www.crunchydata.com/blog/the-many-spatial-indexes-of...

- http://postgis.net/workshops/postgis-intro/indexing.html

- Spatial indexes for OSM in PostGIS (PDF) : https://pretalx.com/media/sotm2019/submissions/CAD93S/resour...