Step 1 :
Divide $2025$ by $513$ and get the remainder

The remainder is positive ($486>0$), so we will continue with division.

Step 2 :
Divide $513$ by $486$ and get the remainder

The remainder is still positive ($27>0$), so we will continue with division.

Step 3 :
Divide $486$ by $27$ and get the remainder

The remainder is zero => GCD is the last divisor $\boxed{27}$.

This solution can be visualized using a Venn diagram.

The GCD equals the product of the numbers at the intersection.