Why do both east and west isogonic lines tilt toward the west as they go north? Here is a picture of the 3 degree east isogonic line just north of Tulsa, OK.


Here is a picture of the 4 degree west isogonic line just east of Nashville, TN.


They both trend westward in relation to true north as you follow the lines northward.  Why do they not go in opposite directions if one is to the east and the other to the west?  This also implies that the 0 degree isogonic line is not parallel to true north.

I checked, and sure enough, it also goes west as you follow it to the north.


Why don't the lines tilt in different directions after crossing over from zero degrees?
Because the present position of the magnetic pole pole is such, that in central and eastern US states the isogonic lines are tilted to the West. But in western parts of the U.S., those lines are tilted to the East...