A market depth chart visualizes a snapshot of an exchange order book as two cumulative step areas around the mid price. Cumulative bid volume rises as a green step area to the left of the mid price (summing buy orders from the best bid downward), while cumulative ask volume rises as a red step area to the right (summing sell orders from the best ask upward). The bid-ask spread appears as a gap at the center, with price on the x-axis and cumulative quantity on the y-axis. This is the iconic chart found in nearly every trading and crypto exchange UI, revealing liquidity, support/resistance walls, and the imbalance between buying and selling pressure.
