1) First define a new scattering brush pattern. Press Ctrl-N for new document, select 30 * 30 pixels. Select pencil tool, brush size 1 px, slect black as colour (0,0,0) and paint two dots like this:
![Image](http://img30.imageshack.us/img30/7008/68666580.png)
Then select Edit -> save brush pattern. Then close this new document and save it if you want (I didn't).
2) In your feature map document, select the pencil tool and then select the brush you just defined (it will be last in the list). Make sure anti-aliasing is off, and that you did indeed select the pencil tool and not the brush tool (the brush tool doesn't work because it blends foreground colour with background), like this:
![Image](http://img233.imageshack.us/img233/7134/30770969.png)
Then, select as foreground colour the colour matching the first feature in fs.txt, normally red 255. Then select as background colour the colour matching the last feature in fs.txt, for me it was red 244.
3) Customise brush options
Press F5 to open the brush options, it should look like this:
![Image](http://img191.imageshack.us/img191/941/44950231.png)
Select Scattering and set a value to about 500% (or experiment yourself). Then select colour dynamics and set foreground/background jitter to 100%. The close the window.
4) Paint the trees. Just spray the dots to where you want the trees. This is the fun part. (I have the texture map superimposed on the featuremap so I can see where I want to paint them).
If you select channels/red you and then histogram up in the info menu, you can see and check that only the relevant red colours are used. It should look like in the picture, lots of red 0 (= black) and then some of the colours matching the feature used.
Hope this is of use to someone/not common knowledge.