#IronViz Recap Part 1: How to Build Trapezium Tile Maps

Jul 6, 2018

Some of you may have seen the #IronVizEurope grand final, where trapezium tile maps (Neil Richards labeled them this way and I quite liked it) for Europe played a significant part in my winning viz on the Big Mac Index.

I had seen a trapezium map only once before in this cool viz by Heidi Kalbe:

While Heidi uses trapezium shapes in a grid, I wanted to use polygon data due to the special #IronViz situation, having no time to figure out the right size of the shapes to make the distances between the shapes look really accurate. With a polygon map I would be able to just bring in the data, set a border and go for it.

To build a polygon map there are many blog posts and tutorials around explaining how to do it. I personally watched this tutorial from the Tableau website. Basically you just need X,Y-coordinates and a point order to tell Tableau in which order to connect these coordinates.

To build my map I first sketched it in Powerpoint:

Looks nice.

Then I needed just a little bit of geometry. I built my trapezes out of three equilateral triangles what allowed me to calculate the coordinates of my trapezes in excel very easily:

1. An equilateral triangle has all sides the same length. The altitude of the triangle can be calculated as shown below.
   
2. Taking three of them looks like this…
   
3. …resulting in these exemplary coordinates:
   

To get all the coordinates I just lay a grid on top of my sketch. So I was able to calculate all the coordinates for any given l.

The rest is just bringing the data to Tableau and creating the viz:

After some formatting it looked like this in my viz (Interactive version on Tableau Public):

Feel free to use my Europe trapezium tile map to create own ones and bring it to the next level! You can find the data here: Data Europe Trapezium Tile Map.