So, I’ve got this forest that I’m making, and I’ve tried weight painting the sides to full blue so the pine trees don’t show up there. Is there any way I can set the faces to a certain weight without the inaccuracy of hand-painted weights? I’m looking for something along the lines of going into edit mode, selecting the faces, and entering a weight value.
Vertex weight is a property which belongs only to vertices. It gets interpolated linearly across the edges and faces of a mesh. So if one vertex has a weight of 1.0, and its neighbors have 0.0, the faces will have a smooth gradient of weight across them, just like how it appears in weight paint mode.
You can assign weights just as you described in edit mode, by selecting the vertices in and assigning them to the vertex group using the Assign and Remove buttons in the Vertex Group section of the mesh properties. The weight and resulting particle density will still be interpolated though, so try removing the outermost edges at the top of your earth surface.
EDIT: Remove them from the group, I mean. or better yet, just split the mesh at that edge. That will create the perfect hard edge you need.
You could also simply split your mesh if it s the one shown on the picture below…