I'll preface this by saying that I don't really know what I'm doing.
To put my question into context, I'm creating a 3D area based on satellite data from the GIS add-on. I want to add randomly distributed trees across the whole area. The way I'm doing it is in Geometry Nodes, where I use the Distribute Points on Faces node to trigger many instances of a tree model. What I want to do, and can't figure out how to do, is to modulate the density input of the Distribute Points on Faces node according to the vertical (Z) position of the ground mesh, basically having an increasing gradient of tree density as the Z coordinate increases. I've tried using a Position node, separating the Z value and linking that to the density, but the position node doesn't seem to actually indicate anything. Here's my (functional) node setup with static density:
The density value shows as 0, but I set it at 0.00001, just to be clear.
Additionally, if anyone knows how to restrict the domain of points to only a specific area, in this case the camera's view angle, that would also come in handy. The camera stays static, so I'm not asking to dynamically update points.