Region Adjacency Graph

## Example Images
![figure_1](https://cloud.githubusercontent.com/assets/3823490/3291718/5ce9b952-f587-11e3-8c29-e2aace6d7794.png)
![figure_2](https://cloud.githubusercontent.com/assets/3823490/3291723/7074b134-f587-11e3-8c73-d28222891a21.png)


I still think you should iterate over `nodes` first, creating the attributes, and then iterate over the array. Since there are much fewer nodes than there are array points, you will save a huge number of if/else statements!

You can also save a dictionary element *and* your final loop through the nodes below by using a [cumulative running mean](http://en.wikipedia.org/wiki/Moving_average#Cumulative_moving_average).