Which one of the following statements regarding the concept of scale is correct?

None of the above.

To determine which one of the following statements regarding the concept of scale is correct, we need to examine each statement and understand the meaning of scale. The concept of scale refers to the proportionate size or measurement of an object in relation to its real-life counterpart or to other objects.

Let's analyze the statements one by one:

1. "Scale refers to the thickness of an object."
This statement is incorrect. Scale does not refer to the thickness of an object, but rather to the size or measurement of an object in relation to its real-life counterpart or to other objects.

2. "A small scale means that an object is small in size compared to its real-life counterpart."
This statement is correct. A small scale indicates that the object is smaller in size compared to its real-life counterpart. For example, a model of a building at a 1:100 scale would be much smaller than the actual building.

3. "Scale is only used in geography and cartography."
This statement is incorrect. Although scale is commonly used in geography and cartography, it is a concept that applies to various fields such as architecture, engineering, design, and art. The concept of scale helps to represent objects accurately and proportionally.

Therefore, statement 2 is the correct statement regarding the concept of scale.