Example of map explained in maptimeLex Introduction to D3.js Web Mapping Through 7 Simple Maps.
https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.5/d3.min.js
https://cdnjs.cloudflare.com/ajax/libs/queue-async/1.0.7/queue.min.js
https://cdnjs.cloudflare.com/ajax/libs/topojson/1.6.19/topojson.min.js