Higher-order programming! This makes it more akin to d3.svg.chord i.e.
it can take "d" and "i" arguments. Thanks for the suggestion, Mike!
Also made "n" and "radius" configurable, too.
Can be used to generate great circle paths. Similar to R's
geosphere.gcIntermediate (in which I discovered a bug, while writing the
test case for this!)
Includes d3.geo.greatcircle().distance for computing the shortest geo
path distance using the Haversine formula.
For a tutorial on using great circles, see:
http://flowingdata.com/2011/05/11/how-to-map-connections-with-great-circles/
Mike Bostock
Jason Davies