Start and finish lines different

[rockey1 0]

Why are the start line and the finish lines  different here in Mexico. When did this start? What is the reason? Was this a Mansell rule? Been seeing this for years, just wondering why and when it all started. Thxs

[f1since08 60]

Start line has to be far enough down to allow the grid to be formed, the finish line is always located opposite the race control building.

[MBKF1 91]

And on the whole it's usually either at the very start of the pit lane. On a couple of occasions it's down the end though, by the start line. (Australia / Monaco / Canada / Brazil)