I saw nothing in there about fitness trackers.
https://www.washingtonpost.com/world/a-map-showing-the-users... is the recent WaPo article titled "U.S. soldiers are revealing sensitive and dangerous information by jogging".
> The Global Heat Map was posted online in November 2017, but the information it contains was publicized Saturday only after a 20-year-old Australian student stumbled across it. Nathan Ruser, who is studying international security and the Middle East, found out about the map from a mapping blog and was inspired to look more closely, he said, after a throwaway comment by his father, who observed that the map offered a snapshot of “where rich white people are” in the world.
This seems to have nothing really to do with Marcus Ranum's blog post that the OP linked to.
