This example illustrates this GeoExamples blog entry. It shows only how to create a base map to be used in the tutorial.
The map is based on this example by Mike Bostock.
Modified http://d3js.org/d3.v3.min.js to a secure url
Modified http://d3js.org/topojson.v1.min.js to a secure url
Modified http://d3js.org/colorbrewer.v1.min.js to a secure url
Changed /mbostock/raw/4090846/world-50m.json to a local referenece
https://d3js.org/d3.v3.min.js
https://d3js.org/topojson.v1.min.js
https://d3js.org/colorbrewer.v1.min.js