Placing different types of Grass I'm trying to place two kinds of grass on a ground plane:


The exposed ground north of the east-west road should have short (Bahia) grass, with a sprinkling of weeds.
The exposed ground south of the east-west road should have long (Rye) grass, again with a sprinkling of weeds.
The ground covered by pavement or water should have no grass or weeds.


What I've read here and in grass tutorials suggests I'll need both vertex and weight groups:


Divide the ground plane into two vertex groups -- a Bahia group from the center of the road north and a Rye group from the center of the road south.
Weight-paint the ground so exposed ground has a weight of 1 and covered ground has a weight of 0. (Call this weight group Exposed Ground?)
Set the Bahia particle system to use both the Bahia vertex group and the Exposed Ground weight group for Density.
Set the Rye particle system to use both the Rye vertex group and the Exposed Ground weight group for Density.
Set the weed particle systems to use the Exposed Ground weight group for Density. If I don't specify a vertex group, the weed particle systems should emit from the entire plane, masked by the Exposed Ground weight group, yes?


Will these steps show tended grass north of the road and wild grass around the swamp in the south, with grass and weed particles emitting only from exposed ground?

Thanks in advance for your help!

Crissie
From what i know there is no such thing as Weight group in Blender.
What you need to do Crissie, is:


Create 3 vertex groups - north(reaching from the edge of the east-west road to the last north most vertex), south (reaching from east-west road edge to the north most vertex), and weed (those two earlier groups combined, so all terrain except the east-west road) and assign appropriate vertices with weight 1 to them.
Use weight paint to cover lake part with weight 0 for south group.
Use the same method to cover road and pavement with weight 0 for north group.
Use the same method to cover road,pavement and lake for weed group
Use north group for Density in Bahia particle system,
Use south group for Density in Rye particle system,
Use weed group for Density in weed particle system.