Here is mapmaking guide:
https://forums.civfanatics.com/threads/guide-to-space-map-making.656681/
It contains mapcategories and list of terrains among other things.
So map category is group of terrains. Terrain may have multiple mapcategories.
I sorted them by distance in mapcategory infos.
MAPCATEGORY_CISLUNAR - Earth neighbourhood.
MAPCATEGORY_MAPCATEGORY_LUNAR - Moon
MAPCATEGORY_SOLAR_SYSTEM - Deep space (entire solar system except Orbit/Cislunar Space/Moon/Mars/Venus/Titan)
MAPCATEGORY_MARTIAN - Mars
MAPCATEGORY_VENUSIAN - Venus
MAPCATEGORY_JOVIAN - Planets (NOT Mars/Venus), moons (NOT Moon/Titan), asteroids and Kuiper belt objects.
MAPCATEGORY_TITANIC - Titan - moon of Saturn.
MAPCATEGORY_INTERSTELLAR - Nearby stars, separates stuff from farther zones.
MAPCATEGORY_PLASMA - Nearby stars themselves
MAPCATEGORY_GALACTIC - General category for transtellar space, stars, Orion Arm and Milky Way - equivalent of Solar System mapcategory.
MAPCATEGORY_MILKY_WAY - Orion Arm and Milky Way
MAPCATEGORY_UNIVERSAL - Extragalactic space
MAPCATEGORY_DISTANT - Universe beyond cosmic horizon - essentially extragalactic space very far away,
MAPCATEGORY_HYPERSPACE - Artificial terrain generated by hyperspace settlers and chronoforming ships.