The north magnetic pole is located close to 71° N latitude, 96°  W longitude and is about 1,300 miles from the geographic  or true north pole, as indicated in  Figure 16-8.  If the Earth  were uniformly magnetized, the compass needle would point  toward the magnetic pole, in which case the variation between  TN (as shown by the geographical meridians) and MN (as  shown by the magnetic meridians) could be measured at any  intersection of the meridians.  line.) An isogonic chart is shown in  Figure 16-9 . Minor  bends and turns in the isogonic and agonic lines are caused  by unusual geological conditions affecting magnetic forces  in these areas.  Actually, the Earth is not uniformly magnetized. In the United  States, the needle usually points in the general direction of  the magnetic pole, but it may vary in certain geographical  localities by many degrees. Consequently, the exact amount  of variation at thousands of selected locations in the United  States has been carefully determined. The amount and the  direction of variation, which change slightly from time  to time, are shown on most aeronautical charts as broken  magenta lines called isogonic lines that connect points of  equal magnetic variation. (The line connecting points at  which there is no variation between TN and MN is the agonic  The true heading (TH) is the direction in which the nose of  the aircraft points during a flight when measured in degrees  clockwise from TN. Usually, it is necessary to head the  aircraft in a direction slightly different from the TC to offset  the effect of wind. Consequently, numerical value of the TH  may not correspond with that of the TC. This is discussed  more fully in subsequent sections in this chapter. For the  purpose of this discussion, assume a no-wind condition exists  under which heading and course would coincide. Thus, for  a TC of 065°, the TH would be 065°. To use the compass  accurately, however, corrections must be made for magnetic  variation and compass deviation.  On the west coast of the United States, the compass needle  points to the east of TN; on the east coast, the compass needle  points to the west of TN.  Variation is the angle between TN and magnetic north (MN).  It is expressed as east variation or west variation depending  upon whether MN is to the east or west of TN.  Figure 16-8. Magnetic meridians are in red while the lines of  longitude and latitude are in blue. From these lines of variation  (magnetic meridians), one can determine the effect of local magnetic  variations on a magnetic compass.  Figure 16-7. Courses are determined by reference to meridians on  aeronautical charts.  Variation  Figure 16-6. Compass rose.  16-6  36  3 3 3 0 27  2 4 2 1 18  1 5 1 2 9  6 3 N N W  $_{N}$$_{N}$ E N E N E S E S S E S W W S W W $_{N}$W N E S E S W $_{ }$N W W N E S 0 6 5 ° 2 4 5 ° Course to B 065°  B  A  Course to A 245°  TN  MN 