An improvement upon the previous experiment. Two alternating concatenation rules (X and Y) are used to make the spiral grow alternatively clockwise and counterclockwise. Due to the fact that less segments are aligned, the worst aspect ratio of this layout is 1/4 like for the Hilbert spiral layout (the former experiment gave 1/6).
Modified http://d3js.org/d3.v3.min.js to a secure url
https://d3js.org/d3.v3.min.js