The x-axis is size of trade, and the y-axis is % of trades at a specific size. ExRates had _many_ large trades, which shows up as a significantly different distribution than other exchanges like Coinbase/Bitstamp/Kraken (which had many small trades, and a long tail of larger size trades). See slide 42-44 here: https://www.sec.gov/comments/sr-nysearca-2019-01/srnysearca2...