Which is an extent of part of a surface enclosed within a boundary?

Which is being described in this picture that is measuring the extent of an object?

Which one is the distance around the circle?

In Geometry, what do you call to the bounding line or curve of a plain area?

What is a number expressed as a quotient of two other numbers in which it can also be a small or tiny part, amount, or proportion of something?

What is the process of changing or causing numbers to change from one form to another?

It serves as a measure of reference.

What is a space inside a solid figure?

Which one is a scale of a measuring tool?