Hmm, not sure if I know exactly what you mean. Typically on a long, transoceanic flight like SFO-SYD it's almost the most direct routing that's flown. Keep in mind the earth is round () so what appears to be a curved line on a map can actually be the fastest distance. I know in many cases it's nowhere even near the fastest direct distance, but in the case of SFO-SYD I think it's pretty close.