How to read a market heatmap like a desk

A heatmap compresses an entire market into one glance: every tile is a company, the tile's size is its market value, and its colour is today's move — green up, red down, deeper colour for bigger moves. That's the encoding. The skill is in the questions you ask of it, and a desk asks them in a fixed order.

One colour or two?

First question: is the whole map leaning one way? A map that is almost entirely green or entirely red is a breadth day — money moving in or out of the market as a whole, usually on macro news. A map split into camps is more interesting, because it means money is moving between things, and the pattern of the split tells you what the market is arguing about.

Is the story sectoral?

On the ASX the two biggest blocks are unmissable: the banks and the miners. When one block is green and the other red, that is almost never company news — it's a macro story wearing company logos. Rate expectations, a China headline, a commodity move, a currency swing. The heatmap shows you the rotation faster than any headline can, because you see the whole cohort move together.

Who's fighting their sector?

Next, hunt the outliers: one deep-red tile in a green sector, or the reverse. A stock fighting its own sector is usually company-specific news — a result, a downgrade, a broker note, a surprise announcement. That's your cue to go read the actual announcement rather than guess.

Intensity, not just direction

Finally, weigh the shade. A sea of pale colour is drift — the market marking time. Concentrated deep colour in one region is a repricing: the market changing its mind about something specific, with conviction. The difference matters more than the direction.

Two honest caveats

A heatmap shows price, not value — a deep-green tile tells you what moved, never whether it should have. And tile area mirrors market value, which means the big end of town dominates the picture. That's a feature, not a bug: it shows you the index's day the way the index actually experiences it, but it also means small-cap stories barely register. If your interest lives outside the top tier, the map will under-tell it.

One more thing: on a delayed feed — ours included, and it's labelled — treat the map as the shape of the day, not a live trading signal. Ten seconds, five questions, and you've read the whole arena.

General information only — not personal financial advice.