How do I render a depth animation?

How would I render just my animation’s depth?

Thanks

What does that mean?

Just the Z channel?

Yeah, I think that’s what it’s called. Incase it is, how would I render that out?

What you’re looking to do requires using a map node and a color ramp node. Take a good look at this image from the online manual and pay close attention to the Map Value node:

Of course, you’ll have to tweak it to suit your particular render

Another way to achieve this effect is to use a Mist pass in the compositing. I had start an animation some time ago with this process, you can see the beginning here.
To do this, enable a Mist pass in the render layers panel, and play with your mist settings in the World Material Panel. Mines are Linear, Start: 0, Dist: 43, Height: 0, MisI: 0.
And here is my node tree.
http://www.bupla.com/blender/mist.jpg
There may be aliasing problems though, but it don’t bother me for my animation style.