Comment by vmaurin

I worked 12y the ad-tech industry, and 3y in a company using this kind of data to measure performance of "drive to store" campaigns: doing online campaign, then seeing if people visit the actual real store based on geo data. The company was actually controlled by the CNIL (French regulator) according GDPR, so we were "anonymizing" data, meaning hashing one way the IFA (unique phone id for advertiser) and storing location within a 300mx300m square I put some quote around anonymizing because geo data from your phone in the evening/night is enough to know where you live (with 300m precision). The rest of the industry in France and Europe was still a far west though (around 2020)