I'm a big fan of the "automagic" JSON visualization added to GitHub (noted in my top ten of 2013) last year. Now, there are some valuable additions:
Starting today, any time you view a commit or pull request on GitHub that includes geodata, we'll render a visual representation of what was changed.
In practice, you see geometry differences via a slider. Move one way see one version, move the other way, see the other. I think Esri and others call it a "swipe tool."
We'll even diff properties within the geometry when they change:
In practice, if attributes have changed (yes, that's the Esri word), you'll see both the old (red) and the new (green).
you can now customize individual features by specifying properties such as the fill color or opacity within the geoJSON file itself