This example uses d3.geo.circle and d3.geo.azimuthalEquidistant to draw rings of constant distance from Sydney.
forked from /mbostock/4436875
Changed /mbostock/raw/4090846/world-50m.json to a local referenece
https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.5/d3.min.js
https://cdnjs.cloudflare.com/ajax/libs/topojson/1.6.19/topojson.min.js