Size & scale

The treemap

Thirteen rectangles, no axis, and one area judgement per comparison.

a.k.a. tile chart · squarified treemap · nested rectangles · the box-in-a-box chart · mosaic plot · marimekko chart

A treemap gives every value a rectangle whose area is exactly proportional to it, and then packs the rectangles together. The arithmetic is impeccable and the job it hands the reader is the hardest one on any chart: area is the product of two dimensions, so nothing you can measure on the page is the value. A tile can be the widest on the chart and the fifth largest, because width is only half of it. There is also nothing to measure against — no axis, no baseline, no gridlines, only neighbours — and the shapes are not even fixed by the data: feed the same numbers to the same layout in a different order and every rectangle changes proportions while its area stays put.

How to spot it

Pick two tiles and try to say which is bigger and by how much. If you catch yourself comparing widths, you have answered a different question than the one you asked.
Look for a wide, short tile beside a narrow, tall one. Equal areas in those two shapes never look equal, and unequal ones routinely look the wrong way round.
Find the axis. There isn’t one — so every number you take off a treemap, you have actually taken off a label.
Ask what order the tiles were fed in. Squarified, ordered, strip and slice-and-dice layouts draw the same data as four different pictures.
Watch the “other” tile. A remainder is often the largest single value on the chart, and it usually gets drawn as a long band along one edge, where it reads as a margin rather than as a quantity.
Count the levels. A treemap is a hierarchy chart; where the data has only one level, the nesting is doing nothing and the area is doing everything.
Tiles too small to carry a label. Anything under about 1% arrives as a sliver, which is what a long tail looks like when it has no axis to lie along.

The fix

If the question is which is bigger and by how much, put the values on one zero-based axis and sort them: a bar chart trades area for length, and length is judged far more accurately than area — which is the whole of the improvement. It costs vertical space and buys a ranking the reader can actually read, plus room to print the numbers, plus the ability to see a remainder for what it is instead of as a band along the bottom. Where the interesting comparison is between a group and a single item, draw the group’s total as its own bar rather than asking anyone to add areas by eye. Keep the treemap for the job it is genuinely good at, which is real and worth having: a hierarchy with several levels and more categories than a bar chart can hold, read for shape and for share-of-whole rather than for rank — a disk-usage map, a budget broken down four levels deep, a portfolio by sector and holding. When you do use one, sort the tiles so position carries some information, label every tile with its number, keep the layout near square and say which layout it is, and lift any comparison that actually matters out of the picture and into a small sorted chart beside it.

In the gallery

Dark navy board slide, masthead “Northwood Sourcing Partners · Supply-base review · Board pack, FY27”, headlined “Five anchors carry the world’s log supply — and Canada is one of them”. A subhead reads: where the wood actually comes from, measured the only way it can be measured — every cubic metre of industrial roundwood the FAO recorded in 2024, all 174 reporting countries, one item, one year, one unit; the twelve largest producers named, the other 162 kept on the chart as a single tile; every area exactly proportional to its volume, nothing sampled, nothing weighted, nothing set aside. Filling the left of the slide, under the label “Industrial roundwood production · FAOSTAT forestry production · 2024 · area ∝ cubic metres”, is a treemap of thirteen rectangles. Across the top row, four tall tiles: a gold United States labelled 319.1, then blue tiles for Brazil 199.7, Russia 193.1 and China 192.4, all four the same height and of similar width. A middle row of seven shorter tiles runs left to right: a gold Canada labelled 114.9, noticeably wider than any of the blue tiles above it, then Indonesia 91.8, Sweden 64.9, Finland 54.6, India 49.9, Germany 47.3 and Viet Nam 45.3, each narrower than the last. Along the bottom sits a narrow, tall Chile tile labelled 42.3 and, beside it, a long band running almost the full width of the chart labelled “Rest of world 540.5 — the other 162 reporting countries”. Down the right-hand side, a gold-bordered card carries 72% over the line “Of world industrial roundwood comes from the twelve named countries”. A card headed “Production · 2024 · million m³” lists United States 319.1, Brazil 199.7, Russia 193.1, China 192.4, Canada 114.9, Indonesia 91.8, Sweden 64.9, Finland 54.6, India 49.9, Germany 47.3, Viet Nam 45.3, Chile 42.3 and Rest of world 540.5. A gold card headed “Read-out for the board” argues that the United States anchors the supply, that behind it sit Brazil, Russia and China and then Canada, whose tile is the widest of that second rank and the obvious home for the FY27 sourcing desk, that the Nordic pair sits well behind Canada, and that the four smallest tiles — India, Germany, Viet Nam, Chile — are a tail that can be left to brokers; it recommends a desk in Vancouver and defers the Nordic desk. A card headed “Why a treemap” says thirteen quantities in one picture, each area exactly proportional to its volume, with no axis to truncate, no baseline to move, no second axis, no log scale and nothing pushed off the chart. A final card, “Basis of measurement”, gives 174 reporting countries, 12 named and 162 in the remainder, one item code, one calendar year, one unit. Three ticked boxes run along the bottom: “Areas exactly proportional. Every tile’s area is its share of world output, to the pixel. No axis anywhere on this chart, so no axis is bent”, “Nothing set aside. All 174 reporting countries are on the chart: the twelve largest named, the other 162 kept as one tile rather than dropped”, and “One unit throughout. Every tile is cubic metres of industrial roundwood, one FAO item code, one calendar year, counted once”. A footnote credits FAOSTAT Forestry Production and Trade, item 1865 “Industrial roundwood”, element “Production”, 2024, retrieved 23 August 2026, notes that China is the FAO “China” aggregate and that Rest of world is the FAO World total of 1,955,737,871 m³ less the twelve named countries, records that the tiles were laid out by the squarified algorithm of Bruls, Huizing and van Wijk (2000) largest first, and states that the slide is a demonstration drawn by us in the manner of a board pack and has never been published anywhere.

The tile that is 15% wider and 40% smaller

The treemap