This map shows “store crowdedness.” Tripadvisor uses anonymized and aggregated “crowd data” in order to show people’s presence in stores and public spaces. This data can be changed based on the time of day and the day of the week. They hope this allows people to make decisions about where and when to visit a particular location.
You can easily pick out industry sites with a large number of employees as well as larger businesses Downtown. Interestingly, many of Detroit’s parks highlight on this map.