# A diagram type for a niche data use case

We would use the principle of small multiples to create a diagram of the same type for each country.an earlier project using the principle of small multiplesIn order to truly reflect the data, the weighting of categories also had to be taken into account..We were inspired by a previous project, where a variation on a pie chart showed the two dimensions of weighting and category value simultaneously, exploiting both radius and central angle.an earlier project playing with geometric dimensionsDeveloping upon these inspirations, we recognised that by shifting the origin of the diagram from a point to a standardized radius, we could encode both negative and positive values..This small innovation gave us the room to represent the data.the moment of inspiration captured in a sketchIn a way, the result is a hybrid of a polar area chart and a pie chart, focusing on deviation from a group mean..We call it a radial mean deviation diagram.With this diagram type, we can show the price for each category with the radial distance from the mean, as well as the weighting of that category with the central angle..Slices pointing inward correspond to a below-average index value, and those pointing outward represent an above-average, or ‘expensive’, index value.Building the diagram with dataWith a concept set, it was time to move on to building the diagram with the real data..We used an unusual but fruitful workflow, generating the SVG structure of the diagrams in JavaScript with D3, before exporting to Adobe Illustrator.Where code is better, we let D3 do the work, where the human touch is necessary, we took the job back.the output of the D3 scriptThrough the many iterations of our analysis and design process, the instant, accurate changes made possible by programming were ideal for rapid prototyping and development of design..For us though, this output does not mark the end of the process.Bringing it all togetherWe decided to create a poster for print from the small multiple diagrams..In the final phase, we were inspired by Vincent van Gogh’s ‘Still Life with Quinces’..On first sight, it looks very yellow but reveals a bounty of colours on closer view..The motif of the still life was a nifty metaphor for the topic of the market basket, too.Still Life with Quinces, Vincent van Gogh 1888For the layout, we decided to sort the countries alphabetically, offering impartiality and easy navigation..Another decision was to forego explicit numbers and use a radial scale of a 20 points per step..Here we declutter the graphic in favour of an intuitive, bigger picture.We highlighted some quirks and outliers, like the fact that Greece is well below EU average in most categories, yet the cost of communication is the highest within the EU.We tested the poster out intensively, following the Nielson Norman Group approach.. More details