To identify location of a town or hill or ship on a map it is necessary to know the coordinates of latitude and longitude. Latitude is determined by measuring  the angle between the horizon and the North star. The earliest instruments for measuring this angle were the "latitude hook" of the Polynesians and the Arab "kamal."  To my knowledge neither is pictured on a stamp.
     The instruments for measuring latitude that are pictured on stamps are the cross-staff, the quadrant, and the astrolabe, the back staff, the sextant and the octant. The cross-staff, also known as the balestila, jackstaff or Jacob's staff was introduced in 1342 by Levi ben Gerson. It has a long graduated staff with a movable cross-member. The eye is placed at one end of the staff, and the cross-member is moved until the lower end touches the horizon and the upper end touches the star or sun.

     The quadrant comes from about the same time. The quadrant is a quarter circle with a scale engraved on the outer edge. The star or sun is lined up on one leg of the quadrant and a weighted pointer marks the angle on the curved scale.

     The astrolabe was known by the sixteenth century. The marine astrolabe is based on the astronomical astrolabe. It is very heavy and, in use, is suspended from a strong swivel thumb-ring. The sights line up the pointer arm with a star or the sun, and the angle is read on the outer ring.

     The astrolabe can either be sighted directly at the sun, or the shadow of the sun can be measured indirectly. The illustration is from Willem Blaeu's The Light of NavigationI, 1612.

      The problem with these instruments is that the navigator may have to look directly into the sun, with the result that over time eyes are damaged. Some people say this is how pirates came to wear their famous black patches – they went blind staring at the sun! 

     "Before the Back-Quadrants were invented when the Forestaff was most in use there was not one Old Master of a ship amongst twenty but what was blind in one Eye by daily staring in the Sun to find his Way."  The cross staff required that one look directly into the sun to take measurements to determine its elevation above the horizon. With the back-quadrant or back-staff one stood with his back to the sun and determined the elevation by a reflection in a mirror.

     The sextant is a modern adaptation of the earlier instruments for determining the latitude.