Well lets say you have a perfect 10,000 sq km, 100 km long and 100 km wide.
You make a straight going from 1 end to the other, say...50 meters wide(or .05 KM wide) and make a quick, 180 degree turn and a straight that goes allll the way back, does another 180 degree turn... over and over and over.......
2000 times.
That track would be 200,000 KM long for just 1 lap.
BUUUUUTTT Nobody is ever ever ever ever going to make a track that boring and utilize literally every square inch of land.
edit- if you used every square centimeter of a 100 sq km track, using the same porportions above...
10 km straight, quick 180 turn at .05 km wide, repeatedly, you could have a 2,000 KM long lap.