The DOM and the heatmap show the same data. The difference is the axis. A DOM is one snapshot of the order book, refreshed constantly, showing you what is resting right now. A heatmap is those snapshots laid side by side over time, so what you lose in precision you gain in memory.
| Bid | Price | Ask |
|---|---|---|
| 5252.75 | 1240 | |
| 5252.50 | 190 | |
| 85 | 5252.25 | 110 |
| 220 | 5252.00 | |
| 165 | 5251.75 |
What each one is actually good at
The DOM is better for now. Exact sizes, exact prices, and the speed at which they change. If you need to know whether the offer is 1240 or 140, the ladder tells you and the colour scale does not. Fast changes read better on a ladder too, because your eye is looking at one column instead of scanning a field.
The heatmap is better for context. Whether that offer was built or dumped, whether the level has been defended before, where liquidity sat before it moved. None of that exists on a DOM, because a DOM has no yesterday and no thirty seconds ago.
The DOM answers "what is there?". The heatmap answers "how did it get there, and has it held before?". Traders who argue about which is better are usually asking only one of those questions and assuming everyone else is too.
Using them together
The practical workflow is to let the heatmap choose the level and the DOM time the moment.
- Heatmap first, at rest. Before price gets there, scan for levels holding persistent size, and for prices where liquidity has repeatedly appeared. These are your candidates.
- DOM as price arrives. When the market reaches one, the ladder shows you what is actually happening to it in real time: whether it is depleting, refilling, or being pulled.
- Heatmap again afterwards. Once the level resolves, the streak records what happened, so the next approach to the same price is informed rather than a fresh guess.
Put them on the same price axis, side by side, at the same scale. Most of the difficulty people have combining the two is mechanical, not analytical: if the ladder and the heatmap are at different zoom levels you are constantly translating between them, and the translation is where the mistakes happen.
When they disagree
They cannot really disagree, since they are drawn from the same feed, but they can appear to, and the appearance is informative.
The DOM shows size the heatmap has barely painted. The order just arrived. That is a level with no history, placed as price approached, which is exactly the profile of an order more likely to be pulled than filled.
The heatmap shows a long streak the DOM says is now small. The level has been taking fills. It defended, it is being worn down, and the question is whether it refills.
The heatmap shows repeated bright levels the DOM never confirms. Size that keeps appearing and vanishing before you can act on it. Read the previous lesson on walls: this is display, not commitment.
Adding the heatmap to a DOM setup does not mean taking twice as many trades. It should mean taking fewer, because a level that looks good on the ladder and has no history behind it is now visibly a level with no history behind it.
Neither one is the market
Both tools show resting limit orders, and resting limit orders are the part of the market that has chosen to be visible. Icebergs hide size, participants pull before they are hit, and a great deal of volume trades from participants who never post anything at all. Use the book to understand where liquidity is, and the tape and the footprint to understand what is being done to it.
The DOM tells you what the book says. The heatmap tells you whether it has been telling the truth.