The GCD of given numbers is 33.
Step 1 : Find prime factorization of each number.
$$\begin{aligned}363 =& 3\cdot11\cdot11\\[8pt]1254 =& 2\cdot3\cdot11\cdot19\\[8pt]\end{aligned}$$(view steps on how to factor 363 and 1254. )
Step 2 : Put a box around factors that are common for all numbers:
$$\begin{aligned}363 =& \color{blue}{\boxed{3}}\cdot\color{red}{\boxed{11}}\cdot11\\[8pt]1254 =& 2\cdot\color{blue}{\boxed{3}}\cdot\color{red}{\boxed{11}}\cdot19\\[8pt]\end{aligned}$$Step 3 : Multiply the boxed numbers together:
$$ GCD = 3\cdot11 = 33 $$This solution can be visualized using a Venn diagram.
The GCD equals the product of the numbers at the intersection.