A liquidity heatmap draws the order book over time: price on one axis, time along the other, and the brightness of each cell showing how much size was resting at that price at that moment. Bright lines are large resting orders that held their place.
What a level is worth
A wall of bids looks like support, but it's only worth anything if it is still there when the price arrives. Watch what it does as price nears. Orders that hold and get traded through mean real intent. Orders that vanish just before being reached are often there to mislead, a practice called spoofing, and they're a reason never to read a static snapshot on its own.
Two different heatmaps
A liquidity heatmap shows real orders that were placed. A liquidation heatmap shows estimated levels at which leveraged positions would be force-closed. The second is a model built on open interest and assumed leverage: useful for spotting crowded zones, but no actual order sits at those levels until the liquidation happens.
Trade bubbles
Many heatmaps overlay trades as bubbles. A bubble that appears exactly at a wall with no change in price is the wall doing its job, and the next lesson has a name for it.