Even car sat nav is an iffy subject. If you car has a data connection, there's good odds that someone is harvesting that data.
For example, I've heard GMC happily sells OnStar data to the lowest bidder - it comes anonymized and aggregated but it's hard to believe they aren't collecting it in a less anonymous fashion.
Garmin’s very solid at keeping your info private from most third parties. Should be safe from anything outside of a valid law enforcement request as long as you aren’t syncing with another service.