Predicio, a French data broker who was caught selling location data harvested from ordinary smartphone apps to the US defense contractor Venntel, also provides 'foot traffic data' in partnership with Aspectum, another US company who sells to law enforcement and homeland security.

Aspectum (aka EOS Data Analytics) claims to provide 'geospatial insight based on cell phone activity and other data sources for a better understanding of local social interaction hazards' such as 'demonstrations, protests, riots, and other mass civil disorder acts', for example.

Sources:
https://aspectum.com/industry-public-safety/
https://aspectum.com/data-on-demand/ 

As a part of a 'combined offer from Aspectum and Predicio', that 'enables' clients 'to track and analyze human activities', 'foot traffic data' is 'available for selected countries' including the US and most EU countries.

So-called 'foot traffic data' usually refers to commercial location data secretly harvested via smartphone apps, often tied to unique personal identifiers.

According to Aspectum's website, Predicio seems to be their main provider for location data, but this must not be true.

"The real-time map displays current protests hotspots, estimates numbers of participants by city..."

Here's how Aspectum has visualized Black Lives Matter demonstrations in June. It's not clear whether they included smartphone/location data here, though: https://aspectum.com/blog/aspectum-visualized-black-lives-matter-protests/

Promo video on YouTube that shows how Aspectum and Predicio identified 75 individuals who met on a train platform in Paris, and then tracked 'their movements around the city during the next 2 weeks', where they 'crossed paths with 100000 other users':

Here's the recent investigation by @martingund that describes how Predicio obtained location data from weather+navigation apps and sold it to Gravy/Venntel, the US firm who is selling location data to US federal agencies:
https://nrkbeta.no/2020/12/03/my-phone-was-spying-on-me-so-i-tracked-down-the-surveillants/

Thread:
https://twitter.com/WolfieChristl/status/1334839943957516289