Sometimes the coach makes the decision as to when and who changes lines. Most of the time the players will change on the fly(which means they change while play is going on). That is when the coach decides the line that goes on but not when. The coach chooses when only during a stoppage in play.
Two points determines a line
wrap
It is made into the liquid line and the entire line has to be replaced.
noone determines it. If it's made in the U.S then, well, its made in the U.s
International date line
The international date line is measured approximately from the 180 degree median longitude line. This is an arbitrary line that determines when a date change takes place within the day.
change in elevation and change in density
the boss
Yes, the world "linear" and "line" have the same root.
chemical change
Only two points.
If by format you mean extension, the thing that determines it is the application it was made with/opens with.