Field note · March 19, 2024
The chart builder is live, and it refuses to do things
What we deliberately made impossible, and the argument we had about one of them.
First tool is up: a chart builder that runs on any dataset here.
The interesting design decisions are all subtractive.
No dual axes. Not as a default — at all. Two y-scales on one chart invite the reader to infer a relationship from where the lines cross, and where they cross is determined entirely by the two ranges you picked. This was the one real argument; the counter-position was "sometimes users need it". They do not. They need two charts.
Bars always start at zero. Length encodes value; a truncated bar axis lies about the ratio. Line charts can truncate, because position rather than length carries the value there.
Categories sort by value. Alphabetical sorting makes the reader do the ranking.
Eight colours maximum, three on scatter. In a bar or line chart only adjacent colours need to be distinguishable. In a point cloud every pair ends up side by side somewhere, so all pairs must separate — and no eight-colour palette does that. Past the cap, series fold into "Other".
A table view under every chart. Not a nicety. It is the accessible fallback, and it is the relief for the palette slots that sit below 3:1 contrast in light mode.
The palette itself was chosen by running a validator that simulates colour-vision deficiency and measures perceptual distance between every pair we might show together, not by looking at it. I have reasonable eyes for colour and I would have got it wrong.
The tool is deliberately a little annoying. Every constraint in it corresponds to a chart I have seen mislead someone.