You measure the perimeter instead of the area when you want to know?

What the size of the border is. Example. You want to fence your yard. What do you do. Measure the perimeter aka the border.

When you want know the distance around the shape rather than how much is inside

I’m not absolutely sure but i think it’s 7x6x5x4x3x2=5040 because as the first character you can take any of the 7 given then you are left with 5 then 6 then 4 etc.