Slides from March d3.js talk at Pivotal Labs are in the .key and .pdf files
This talk teaches how to make this type of long-form interactive created by the New York Times.
Three key concepts:
getPointAtLength()(example1.html / example2.html / example3.html)
Stroke-dasharray(example2.html / example3.html)
getTotalLength()(example1.html / example2.html / example3.html)
An additional explainer can be found in this gist.
Links from the talk
[Example of an interpolation] (http://jsfiddle.net/c5YVX/8/)
[Explainer on stroke-dasharray] (https://source.opennews.org/en-US/articles/animating-maps-d3-and-topojson/)
[Airplanes example] (http://www.tnoda.com/blog/2014-04-02)
[Tween between paths] (http://bl.ocks.org/mbostock/3916621)
[Example of getting the point on a line from any position] (http://bl.ocks.org/mbostock/8027835)