The earth is a not sphere.
Here is a trick ... open google earth. Go to view>reset>tilt and compass.
Now everything is completely straight. North is straight up South straight down. On the Top right corner is a circle that has the North symbol on it. Do not touch it. Under that is the "click to move around" circle. Without touching the up or down arrow on touch right or left and then as the globe spins in its upright position you will see north change. Once you make one revolution North will again be back to the top.
There is true north and magnetic north. When I was in the Navy we were given TWO headings to steer by. We were told magnetic and true north headings and had instruments to monitor both.
On your maps your seeing a 2d version of a 3d, tilted,
oblate spheroid world. Ever noticed map contacts that may say "course 270" and they are not going flat to the left side of the map? They are going heading 270 but you think they are not since they are not following a parallel course to the latitude lines. The lines are not drawn with the curve of the earth in mind.
http://en.wikipedia.org/wiki/Oblate_spheroid
http://en.wikipedia.org/wiki/Oblate_...al_coordinates
... but this is a guess