7. In the Cartesian coordinate system, there are four fixed points $A(-3,0), B(1,-1), C(0,3), D(-1,3)$ and a moving point $P$. Then the minimum value of $|P A|+|P B|+|P C|+|P D|$ is $\qquad$.
Since $A B C D$ is a convex quadrilateral, then $|P A|+|P B|+|P C|+|P D| \geqslant|A C|+|B D|$ $=3 \sqrt{2}+2 \sqrt{5}$, equality holds when point $P$ is the intersection of diagonals $A C$ and $B D$. Therefore, the minimum value of $|P A|+|P B|+|P C|+|P D|$ is $3 \sqrt{2}+2 \sqrt{5}$.