For each hexagon in the tiling, draw its rectangular coordinates. The Y coordinate identifies the row, while the X identifies a sort of zig-zag column.
This type of coordinate system is widely used to address hexagons in a tiling, but has a drawback: It is not possible to interpret the coordinates of the hexes around the origin as unit vectors, therefore it is not possible in general to sum them to an hex position vector to obtain another one.
Compare with another take on hexagonal coordinates, which solves the problem.
Two example hexagons are also highlighted, to show the possibility of addressing an hexagon by using its coordinates.
Modified http://d3js.org/d3.v3.min.js to a secure url
Modified http://d3js.org/topojson.v1.min.js to a secure url
https://d3js.org/d3.v3.min.js
https://d3js.org/topojson.v1.min.js