Spatial files are the geometry under the map. The coordinate system is how planets and fleets are placed; without it, a position is just a pair of numbers with no meaning. This folder is small on purpose — one canonical system, not a gallery of maps.
If you need the schema that describes spatial objects, that lives under visual schemas. If you need to move a fleet, that is the planets and fleet skill, not a coordinate primer.
Open spatial when you are rendering a map, interpreting a position, or writing something that must agree with the client’s coordinate system. If you are deciding whether to relocate, read planets first.