why use euclidean distance in the function for defining weights? Doesn't it mean cities that are farther in distance with fewer friend connections would get a higher weight than cities that are close by? Not sure how it helps visualize or how to interpret it.
Presumably they're using euclidean distance to scale down the brightness of long-distance links -- to ensure that long-distance relationships don't overpower short ones in the visualization. Otherwise, a pair of friends thousands of miles apart would be contributing the same "energy" to the image as a thousand pairs a few miles apart... You'd never be able to see local detail in the areas heavily crossed by global connections (e.g. the Caribbean).
