Slope:
	We left off here last time
	4 directions for slope:
		x axis
		y axis
		each diagonal
	So each point has 4 slopes
	Edges:
		Might be the edges is not in the dictionary
		dictionaries have fast membership testing

We could have interpreted each point as having 8 slopes
	1 for each direction from the center

Color over a certain slope:
	Maybe gray for rocks

Next thing:  Octaves
	How smooth are hills really?
	local gradients

A note about slopes:
	Dirt can slide off the rocks
	Water causes erosion, especially on slopes
	Water at the bottom of a slope especially causes erosion
	How could we make slopes get steeper if they go into the water?

First:  Where is the water, anyway?
	If we have a face, we can tell if it's at water level
	If a sloped face is partly underwater, we could make it vertical
	Great, for limited resolution

Second:  What does "away from the water" mean?
	We can answer this by assuming our face points generally up
	Let's move each face that touches the water away from the water
	Let's color eroded locations so we can see them

Third:  Could we make a a list of locations that need to be eroded?
	Sure
	Less affect at each level

Then all the faces in the list need to be moved

Next lab:
	Kinda depends where we get on this
	Generally:  "Make it look like a different biome, with an animation of the sun passing overhead"