The history of cartography is largely that of the increase in the accuracy with which these elements of distance and direction are determined and in the comprehensiveness of the map content In this development cartography has called in other sciences to its aid For example instead of determining direction by observing the position of a shadow at midday or of a constellation in the night sky or even of a steady wind use was made of terrestrial magnetism through the magnetic compass and instruments were evolved which enabled horizontal angles to be calculated with great accuracy 