Take the age structure and paint it as a grid: every cohort gets a row, every session gets a column, and the colour reports how much of the supply that cohort was holding.

Slanting stripes are groups climbing through the bands as they get older, and those stripes are the entire reason this exists. Every other decision about how it looks was made to keep them legible.

What it actually measures

A vivid slant marks a substantial parcel that traded all at once and has not stirred since. Growing older carries it from one band to the next, drawing a stripe across the grid that no other arrangement of these figures will give you.

Following a single cohort through its whole life is the thing a set of stacked lines cannot do. On a line chart that same group appears as a rise in one series and a fall in another, and connecting the two is left to the reader.

Colours are anchored once to the entire record rather than to whatever happens to be displayed, so a given tone reports the same quantity regardless of the window. Zooming alters how much you can see and never what any of it signifies.

Blank cells are a claim the data never made

Early cells for the oldest cohorts are left empty rather than painted as zero. A ten-year band cannot hold anything before the network is ten years old, and there is a real difference between no supply in a cohort and no such cohort yet.

Filling those cells with zero would be the easy choice and it would quietly assert something false, at the exact corner of the map where a reader is most likely to draw a conclusion about long-run structure. Leaving them blank is the small honesty that keeps the early history readable.

The Age Pyramid: a line answers how much, and a pyramid answers what shape

Each band is a slice of supply by how long it has sat still, drawn against its neighbours rather than against a scale. What the eye picks up is the relationship between adjacent bands, which is exactly what matters.

Supply by age can be plotted as a set of lines, and most dashboards do. That form answers how much sits in each band and makes comparison between neighbouring bands surprisingly hard, because each line has its own path and its own scale in the eye.

The pyramid puts the bands next to each other so a cohort that is unusually large relative to its neighbours is obvious without measurement. That is the property that decides whether supply arrives in a wave or a trickle, and it is close to invisible in the line version of the same data.

What it does not tell you

A heatmap is poor at precise values. It shows structure and relationship extremely well and asks you to go elsewhere for a figure, which is the trade every map of this kind makes.

Cohort shares also move for two reasons that look identical. A band’s share can rise because coins aged into it or because supply left every other band, and the colour cannot separate growth from everyone else shrinking.

Diagonals also fade rather than end cleanly. A cohort dispersing gradually leaves a streak that thins out, and deciding when it has stopped mattering is a judgement the map does not make for you.

How to read it

Young Float. Supply has shifted into the youngest cohorts.

Aged Float. The bulk of the coin has gone untouched for more than twelve months.

Maturing Cohort. Coins are ageing into the middle bands.

Balanced Structure. No cohort dominates the distribution.

Where the Supply Sits runs on the Supply dashboard next to The Age Pyramid, Supply by Vintage Year and Supply Circulation Map.

Common questions

What is drawing the slanted lines?

A single group climbing through the bands as it gets older. A vivid slant marks a substantial parcel that traded all at once and has not stirred since.

Does a colour keep its meaning when I zoom?

Because colours are anchored once to the entire record rather than to whatever is displayed. A given tone reports the same quantity on a narrow window and on the lot.

Why is the top-left corner empty rather than nil?

Because a group that had no way of existing yet is left blank. Filling it in as nothing at all would assert something the record never said.

What can a heatmap not do well?

Precise values. It shows structure and relationship extremely well and asks you to go elsewhere for a figure.

Why can a band’s share rise without coins ageing in?

Because share is relative. A band can grow because every other band shrank, and the colour cannot separate the two.

Why a demographer’s chart instead of lines?

Because what matters is the arrangement taken as a whole. A demographer’s chart makes it instantly plain whether one group towers over the ones beside it, which is precisely the question being asked.

Can the shape ever turn upside down?

Through long uneventful stretches the seasoned bands can outgrow the fresh ones, which describes a supply base that is both patient and very hard to buy from.