Clarify explanation of insertion algorithm

[donkirkby]

Love this project. The only thing I struggled with was the explanation of insertion.

When a new point is inserted into a D3 quadtree...

I don't know the algorithm, so I can't offer a clearer explanation, but are you sure that you're always using N correctly? Is a leaf node a rectangle or a point?

[jimkang]

Hmm, yeah, that section needs a lot of work, and probably more space, now that I think about it. Thanks for bringing that up.

All of the nodes, leaf or not, have some rectangular territory. A leaf node has a point whereas non-leaf nodes never have points directly, but rather, children that may have points. So, what I was trying to say there is that when a new point is inserted into a territory covered by a node, n, that happens to be a leaf, what happens is:

1. n becomes a non-leaf. Its point is removed.
2. n gets a child node.
   • That child node is basically a copy of what n used to be: It's a leaf node with the point that n used to have.
3. A new child is added to n that has the new point.

I'll take a shot at rewriting that this weekend, hopefully!