Graphviz/PyDot and huge graphs

[moriarty]

I have been told that generating the dtree graph of all the samples from the letter data seems like it works, but the graph isn't visible, although mouse over seems to highlight the graph as if it is there.

I forgot to investigate this and am creating this issue to remind me.

The first results from a google search:

• http://www.graphviz.org/content/root
• http://www.embeddedcomponents.com/blogs/2013/12/visualizing-software-tree-structures/