Compass Rose

It was during the Age of Exploration that cartographers began to implement a common standard depicting compass headings in relation to the representation on the map.  This new innovation was often referred to as the "Compass Rose".

A compass rose is a figure displaying the orientation of the cardinal directions, north, south, east and west on a map or nautical chart.  It is also the term for the graduated markings found on the traditional magnetic compass.

Today the use and idea of a compass rose is found on or featured in almost all navigation systems, including nautical charts, NDB and VOR systems, some GPS sets and similar.  In ancient times, however maps were typically drawn from whatever perspective the map maker preferred, and North was rarely aligned with the top edge.

Rose of the WindsAlthough a compass rose may sometimes be called a wind rose, it should not be confused with the graphic tool used by meteorologists to depict wind frequencies from different directions at a location.  A Rose of the Winds (right) is actually an ancient version of a compass rose which personified compass directions as winds with individual names, such as the west wind Zephyrus and the east wind Eurus. 

On these designs, north is traditionally indicated with a "fleur de lis" symbol, while East (with its religious and cosmological significance, the direction of Jerusalem) is often marked with a Maltese cross, as it is seen in the graphic below.

Shown on the left is a replica of a 32-point compass rose from a chart by Jorge de Aguiar (1492), the oldest personally signed and dated Portuguese nautical chartNaming all 32 points on the rose is called boxing the compass.

The "rose" term arises from the fairly ornate figures used with early compasses. A fleur-de-lis figure, evolved from the initial T in the north wind's name Tramontane, is sometimes used to indicate the north direction. Similarly, on old maps the east was marked with an L for Levante, or with a + indicating the direction of Jerusalem from the point of view of western Europe's countries.

Early roses were depicted with 12 points at 30° each, as was favored by the Romans. In the Middle Ages map makers moved to the 16-point rose complaining that sailors did not have the education to understand the previous design. The 16-point rose has the uncomfortable number of 22 1/2° between points, but is easily found by halving divisions and may have been easier for those not using a 360° circle. Using gradians, the sixteen-point rose will have exactly twenty-five gradians per point in.

Kâtib Çelebi’s Cihannuma (Universal Geography), published in 1732, included this illustration of a compass and a sundial.The earliest known examples of a 32-point compass rose was developed by Arab navigators during the Middle Ages. 

An example of an early Arabic compass rose is shown on the right.

In the classical world, no distinction was made between the directions and the named winds emanating from them. Wind names were not standardized (not every region in the classical world experienced the same wind coming from the same direction) and vary by the literary source (though names are relatively more standardized for the four cardinal directions).  Of note, a fountain in Taranto, Italy was inspired by and named after the Rose of the Winds.

The modern compass rose appears as two rings, one smaller and set inside the other. The outside ring denotes true cardinal directions while the smaller inside ring denotes magnetic cardinal directions.

True north refers to the geographical location of the north pole while magnetic north refers to the direction towards which the north pole of a magnetic object (as found in a compass) will point.

The angular difference between true and magnetic north is called variation, which varies depending on location. The angular difference between magnetic heading and compass heading is called deviation which varies by vessel and its heading.

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