 A liquidity heat map, also known as an order book heat map, is simply a visualization of the limit orders within an order book or a financial instrument. Because both current and historical limit orders are visualized, the heat map adds a time dimension to a standard DOM or current order book. This allows you to see the evolution of the order book and the change in order flow over time. In this example, dark red areas represent high liquidity and blue or black areas show low liquidity. It's important to note that a liquidity heat map is not an indicator. Just like price and volume information, the heat map represents raw market data and provides information on the actual behavior of market participants and trading algorithms.