A couple of things that would be nice
- not terrain and not feature tags
- spawn location on river with perhaps a cannot move away from river function too. for all those crocs
- location on fresh water coast - probably the same thing as on river.
Edit thinking on it those last two are plots with "fresh water" present. Which would be enough for my needs.
That cannot be done in the spawn system code, but needs to be a new general unit movement restriction (so a unit tag, not a spawn tag), but shouldn't be hard to do.