Diversity by Color ID not working

[scott]

Inspired by the latest tutorial, I set out to create my own bio wall using color ID for diversity.

It hasn't worked well.

First, I created the wall seen in the image and it wasn't working when I went to set the color ID bitmap.  When I went into another scene and re-opened this one, it was suddenly working.  Weird.

However, the wall on the right is a new attempt to create a patterned biowall.  All I get is this sort of random splotchy mess.  In other words, I have no idea why the first biowall is now working, but the 2nd one isn't.

Next, I have a flat biobed.  This isn't working at all - only 1 color of the ID is showing up.  It's incredibly infuriating, lol.

Okay, what am I doing wrong?   Am I forgetting some vital step that I accidently did the first time out?

[scott]

Basically some further tests show that when I create a simple rectangular plane it MIGHT work.  Any sort of spline and it never works...

[iToo]

Please note Diversity map requires UV coordinates to work, which are taken from the underlying surface.

So you must assign at least a Surface in Forest. There are not problems to use Spline areas as well, but always combined with a Surface.
To avoid that Forest scatters items along all the surface, just turn off "Surface Area" in the Areas rollup.

When there is not a Surface, Forest generates its own (fictional) UV coordinates from the Distribution map settings. These are used for other Forest features, but generate wrong results with Diversity maps.