Every face on a terrain mesh can be locked in height and material, when it was painted with material from the AREAL3D materials.
This is very useful for modelling the terrain, where some areas can be fixed and you can keep on modelling around without touching fixed areas.
Streets and wqlkways are generally locked for some functions.
They can be changed, of course, from a context menu of some tools.
Locked areas are displayed in a darker color.
