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)