In this chapter, the narrative is still third-person omniscient.
The night after the storm (the one that happened back at the end of Chapter 40, which broke up the fight), Captain Ahab goes down to his cabin, takes out a bunch of yellowing sea charts and studies them carefully, comparing them to old log-books and marking them up with a pencil.
While he does this, the lamp overhead swings back and forth, making lines appear on his forehead just as he is drawing lines on his charts. (Hmm, where else did we see a swinging lamp? Oh, right, in Father Mapple’s sermon on Jonah in chapter nine.)
Ahab does this pretty much every night, using charts of four oceans to try to correlate the currents and tides, the location of sperm whale prey, the hunting season, and Moby Dick’s past habits, so that he can figure out where and when he’ll have the best chance of finding the White Whale.
He is totally, as Melville likes to say, monomaniacal.
The narrator assures us that, even though it seems completely insane to try to find one particular whale by searching all the oceans, it’s actually possible to track a lot of variables and make some educated guesses about where sperm whales as a species will be, especially since they often migrate in straight lines in known positions.
Basically, says the narrator, the ocean’s crisscrossed with whale freeways.
Of course, although you can be pretty sure there will be some sperm whales on certain "freeways" in a particular season, you can’t always be sure that it will be a certain individual whale.
Moby Dick has been in four different places in the same season for the past four years.
Still, during the height of the whaling season, Moby Dick appears to hover around the equator: that’s where most of the "deadly encounters" with him have happened, including Ahab’s leg-severing mishap.
The Pequod left Nantucket at the beginning of one whaling season, so Ahab’s spent the last several months sailing south through the Atlantic and heading toward Cape Horn so that he can go through the Indian Ocean and past the islands of Southeast Asia into the Pacific in time for next year’s season.