This heatmap is replayed directly from a real Betfair Streaming API delta feed — the 18:27 Doncaster Arab (GBR) WIN market on 2 May 2026. The Streaming API sends delta messages: only changed price levels are transmitted rather than the full book each time. The processor here replays those deltas to reconstruct the full order book state at each point in time, then samples a snapshot every 4 seconds. Time runs left-to-right on the horizontal axis; Betfair tick prices run bottom-to-top on the vertical axis. Cell colour intensity represents available volume at that price and that moment — dark cells mean thin or no orders, bright cyan means deep liquidity.
In the pre-race period (before the green race-start line), liquidity builds as the market matures — you can see volume concentrating in a tight band of 3–5 ticks around the Last Traded Price. The LTP trace (cyan line) shows the market's direction. At and after the race start, remaining orders are withdrawn and the book collapses rapidly. Select any runner using the tabs above; toggle between back-only, lay-only, or combined views; and adjust the time window to zoom in on specific periods. Steam events — where the LTP moves sharply in a short window — are visible as rapid LTP line jumps.