Dotmetrics is a big data system that keeps track of online web publishers' traffic. We currently operate in 6 countries where we measure over 500 million events on websites and mobile applications daily. Our databases are measured in terabytes, and big data analytics and distributed systems are a daily occurrence. We track users at a device level through a combination of fingerprinting and cookies, which enables precise Unique users calculations. Collected data is unaggregated and at disposal in raw format. This level of granularity gives our users endless opportunities – to slice and dice data in any way. Giving access to data of such granularity significantly impacts the media planning process – enabling media planners to know exactly what impact the addition of a certain website might have for their reach figures. This is used by media planners both to decide on which websites to include existing media plans, or which websites can be excluded, without significant impact on the overall effectiveness of the campaign.