The term “Orientation,” as applied to a structure of any kind, means the direction in which its principal line is laid out on the ground. Originally, as the word implies, orientation signified “eastwardness,” only, and had special reference to churches, because (in western Europe) practically all churches were built with the longer side laid out in an east-and-west direction. In some, the line is to True East, exactly; in others the axis lies at an angle of some degrees either to the northward or to the southward of True East. This divergence in either direction from the Orient is called “the angle of orientation.” Nowadays, the term “Orientation” has lost its original “Eastward” distinctiveness, and has become a general expression merely indicating “direction,” and may imply any point of the horizon, and not necessarily the eastward.
Originally the angle of orientation was measured from True East as a zero, but now it is reckoned from the Meridian, or North (true).