Navmesh painting areas ....

I am trying to set up a terrain whereby my lil minions with use their AI to journey along roads and paths, rather than taking a beeline straight over a mountain.
Looking in the Navigation window and the Areas tab I see that I can set colours to area and the associate a cost to them -this is great - EXCEPT how do i assign the colours to various areas of terrain? Can I paint the hillsides in a certain colour associated with hills and a movement cost of 2.5, sidewalks as another colour and a movement cost of 0.75 to hopefully get them to walk alongside a road?

 

Unfortunately it's not that simple to assign different NavMeshCosts per surface out of the box.
If you take a look at the NavMeshComponents package, you'll see that there are NavMeshModifierVolumes.
Your best approach would be to place these volumes on hill slopes and such to set this up properly.
This is possibly a lot of manual work, so if you think it'd be more efficient to write an editor script for this, you'll probably want to use the Terrain's height map to scan for the right differences and create Modifiers accordingly.

 

eeep - thats not looking fun or easy....