The DOM shows you what the order book looks like right now. The heatmap records what the order book has looked like over time. It is a two-dimensional visualization: price on the vertical axis, time on the horizontal axis, and color intensity representing the size of limit orders sitting at each price and time combination. Hot colors mean large limit orders were present. Cool or empty areas mean thin or no visible book depth.
Reading the heatmap is a skill separate from reading the DOM in real time. The DOM is a point-in-time snapshot. The heatmap is a history of that snapshot at every moment. This makes it useful for identifying patterns that are impossible to see by watching the DOM alone: absorption events, spoofing signatures, and structural liquidity gaps that price is likely to revisit.
What you are actually looking at
The heatmap is a grid. Each row is a price level. Each column is a unit of time (typically one or a few seconds). The cell color tells you how large the limit orders at that price were at that moment. On most implementations, bright blue or white indicates very large limit orders on the bid side. Red indicates large limit sell orders on the ask side. The background shade fills in for smaller orders, and empty or near-black cells indicate minimal book depth at that price and time.
When a large level holds
Absorption on the heatmap looks like a large bid or ask wall that remains visible as price repeatedly tests it and bounces. The wall does not move and it does not disappear. The intensity stays high over multiple time periods. Price keeps touching it and walking away. This is the limit order sitting there and absorbing market orders from the opposite side without being fully filled.
The significance of absorption depends on the structural context. A large bid wall at a VP POC that holds through two or three tests is very different from a large bid wall in the middle of a balance range with no structural reason to exist. Absorption at a meaningful structural level, confirmed by the heatmap showing the wall persisting, is one of the cleaner signals the order book provides.
Price descends to the prior session's VAL. A large blue bid wall appears at that price on the heatmap. Price touches the level twice, bounces both times, and the wall holds. Cumulative delta, which had been falling, stops falling and flattens. The heatmap confirmed a large passive buyer at a known structural level. The flat CD says the seller aggression that drove price down is not accelerating anymore. This is a credible long setup with three independent reads aligning.
Price rallies toward the composite profile VAH. A large red ask wall appears at that level on the heatmap. Price touches the level, pulls back, comes back, touches again, and the wall is still there. Cumulative delta was rising into the level and has now flattened. The ask wall is absorbing buy flow. The level is holding. This is the order flow confirmation that the structural resistance is backed by an actual large passive seller. Valid short setup once price confirms the rejection with a lower close on the footprint.
Large levels that vanish before price arrives
Spoofing on the heatmap is visually distinctive. A very large order appears several price levels away from the current price. It creates a bright hot zone on the heatmap. Price begins to move toward it. Before price gets close, the order disappears. The hot zone goes cold. The price that was supposedly defended by that large order now has thin book depth. Price moves through it with no resistance.
The intent is to create the appearance of a large order to influence other traders' behavior, then cancel it before it gets filled. The heatmap is the tool that makes this visible in a way the live DOM alone cannot, because the DOM snapshot only shows what is there right now, not what appeared and disappeared in the last 10 seconds.
Not every large order that appears and is cancelled is spoofing in the legal sense. Large institutional traders frequently adjust orders as conditions change. The heatmap cannot prove intent. What it can show you is that a large level did not hold when price arrived, which is the practical fact you care about: the apparent resistance or support was not real. Do not trade against price based on a heatmap level that has already shown it disappears on approach.
Empty zones and price magnets
Gaps on the heatmap are areas where the book has been consistently thin across multiple time periods. Very little bid or ask volume sits in that price range. When the market enters a gap, it has minimal limit order resistance to slow it down. Market orders can push through rapidly. Gaps are where fast moves happen.
Gaps also act as magnets. Once price crosses into a gap from a dense area, there is often a rapid move to the next dense area on the other side. This is not random. It reflects the actual distribution of limit order interest: price finds friction where orders exist and moves quickly where they do not. Identifying a gap between two significant levels tells you approximately how far price might travel if it clears the near level and enters the thin zone.
Mark dense heatmap zones as potential support and resistance areas before the session opens. Note the gaps between them. When price approaches a dense zone, watch for absorption or fade behavior. When price clears a dense zone and enters a gap, the target is the next dense zone on the other side. The heatmap makes the likely travel distance visible before the move happens.
Complementary, not redundant
The heatmap and the DOM are answering different questions and neither replaces the other. The DOM gives you the current book in detail: exact sizes, exact price levels, live changes. It is high-resolution but only covers the present moment. The heatmap gives you lower resolution but covers a period of time. Patterns that are invisible in a single DOM snapshot become obvious when you can see the book recorded across minutes.
In practice, use the heatmap for the macro read: where are the big levels, where are the gaps, has the wall held or been pulled on prior tests. Use the DOM for the execution read: is the wall still there right now, is size entering or leaving, is the book stacking or pulling as price approaches. The combination gives you both the context and the current state.