Only you have access to your Footprints map and the detail of the areas you’ve unlocked.
However, your friend(s) can see the percentage of an area you’ve unlocked if all the following is true:
1. your friend has visited the same area at least once
2. you're one of the top 2 friends of your friend who have the highest unlocked percentage of an area
The precise details of where you have visited in each area are private to you only and are not displayed on your friend's map.