Physical and digital objects often leave markers of our use. Website links turn purple after we visit them, for example, showing us information we have yet to explore. These "footprints" of interaction help us navigate information saturated environments – they enable us to easily revisit old information, systematically explore new information, and quickly resume tasks after interruption. The design principles are simple, but have clear benefits. Could they also apply to data visualization?

We propose HindSight – an umbrella term for the design space of representing interaction history directly in existing data visualizations. In this work, we examine the value of HindSight principles by augmenting existing visualizations with visual indicators of user interaction history (e.g. How the Recession Shaped the Economy in 255 Charts, NYTimes). Try some examples yourself in the links above!

In controlled experiments of over 400 participants, we found that HindSight designs generally encouraged people to visit more data and recall different insights after interaction. The addition of HindSight requires little-to-no technical overhead (often just a couple of lines of code), and is based on interactions that are familiar to a diverse set of users. Simple additions to visualizations can significantly impact users' exploration and insights.