That means one might be on your car and someone is tracking you - if it’s tracking you for 200 miles constantly that means it’s with you or on your car / person etc

If it was tracking you for let’s say 1 mile and stopped , than it could of just been one In your vicinity and than you left the range of it

Apple purposely alerts you when an air tag is tracking you (any air tag even if you don’t own one) because of the “dark side” of air tags (criminals use it to rape, stalk , set up , track etc) - so being it’s been tracking you for 200 miles , it’s deft on your car somewhere or in your personal belongings