## Cross Ratio

According to definition:
The cross-ratio $(z_1,z_2,z_3,z_4)$ of four distinct complex number is defined as $\frac{(z_1-z_2)(z_3-z_4)}{(z_1-z_4)(z_3-z_2)}$.

My question is :
1 . What is the geometry view or visualization of cross-ratio? Meaning that, what does it means geometrically?
2 . When will $(z_1,z_2,z_3,z_4)$ remain unchanged if we change the order? e.g $(z_2,z_3,z_4,z_1)$