When Master Chief throws a grenade in Halo, someone is watching. Online games are perfect petri dishes: a controlled space (the game program), with multiple variables (the players), open to observation. First Bungie, Halo’s original developer, and now 343 Industries have kept records of minutia, such as player movement patterns within the game world, for years. As thousands of hours of play accumulate, this data breeds valuable insight: Heat maps that show an unusual frequency of gunfire or grenade blasts in one area will lead to wider corridors, or open doors where once there was only concrete walls. By paying attention to trackable statistics, designers can make sure the next game will flow more smoothly, improving player satisfaction.