I'm sure a lot of people who create worlds knows this so this is more for newer CAW-ers.
I learned this from someone on Custom Sims 3... don't remember exactly who (blush) it can help if you want to make sure you lots are placed on a flat spot.
*I think I have this information correct. If not, please correct me and I'll delete this is shame and humiliation.
Since I'm making a mostly flat world I need to make sure it is as flat as I can make it- Right now I'm working on the hill part.
A. This part-
B. What you need to do now is turn on the Wire Frame. Click View and then click View Wireframe. It will look like this-
C. I keep the brush size small so I don't flatten too much too fast. Use the Flatten- Gentle set high.
D. The brush is hard to see unless it crosses the wireframe lines...
E. Since I want the lot areas to be flat and the lots will be against the roads, pick a start spot at the road~ That will be the height of your level. Keep starting from that area.
If you start leveling again from another area that hasn't been flattened from your first spot- it can be at a different level and not really flat.
F. Slowly move the brush over the area you want flat. The view of the chunk will change when and if it hits an area that isn't level/flat with your starting point.
G. When it flattens or you slowly move the brush over a flat spot the view will change back to the wireframe.
H. Keep going slowly over the area you want at that level. Move it slowly and make sure you hit the areas a few times to test.
The larger the squares/triangles, the more continuous flat area, they get smaller as they go toward an uneven area. You don't have to make the squares large- that's only in large areas of flat land. But you can tell an area is flat by them.
J. Turn the Wireframe off when you're done.
Hopefully I explained it well enough. I'm not always good with explaining.