Calculate node density

[alligitor]

This is not an issue but a feature request.

I was looking at the map and was asking myself, what's the nerdiest region in the world, based on density of nodes.

I think it would be a cool metric to calculate.

A super easy algorithm is:

For every node
    for every other node
        calculate distance
            if distance < X
                count up
density = counter / area (based on a circle of radius X)

The density can then be a gradient color overlay on the map.