How do I make a single face of an object a particle emitter? I have an object which has a particle emitter at the bottom. The entire bottom of it is currently the emitter but I would like to make the middle face the emitter. How would I go about doing this?
You can make Vertex Group out of bottom face (create Group, select Face and hit Assign, without painting)...



...and use it to control Density under Particle System > Vertex Group.