The Magnetic Compass and North Orientation

One of the recurring questions I get is why maps are so uniformly oriented with north at the top. A brief blog post from the Bodleian Library’s Map Room, on the occasion of the near coincidence of the magnetic north pole with the true north pole, asserted an answer to that question. Alas, it’s wrong. The post stated:

We are used to having north at the top of our maps. This has been the most common orientation for hundreds of years, largely because of the use of the magnetic compass.

This statement is an example of the kind of incorrect thought caused by the modern ideal of cartography. Maps are commonly oriented to north in the Western tradition, but not because of the compass, or even “largely” so. An explanation of the practice requires attention to the particulars of each mode of mapping, and not the unthinking presumption that all maps are somehow grounded in the same structural principles (i.e., those of cartography).

World and Geographical Mapping

The placement of geographic/true north at the top of world and regional maps is, in the Western tradition an element of ancient Greek practice. The Greeks had two ways to map “the world” (itself a fluid concept).

First, the common manner of mapping the inhabited world (οικυμενε, ecumene) was as the circle (περιοδοϛ γεϛ, periodos ges, “circuit of the earth”) of the ocean sea enclosing Asia, Europe, and Africa; this tradition perhaps derived from older traditions among ancient Babylonia and Egypt, and certainly influenced Roman mapping, from which medieval mappaemundi stemmed in turn.

Second, a few scholars applied the astronomical practice of dividing the skies by lines of latitude and longitude to dividing up the earth, culminating of course in the world maps described by Claudius Ptolemy in the second century CE. Off the top of my head, I don’t remember if Ptolemy explained why he oriented his maps of the ecumene with north at the top, but the geometry of their construction and the need to have the ecumenical maps—wider than broad—lie along a papyrus scroll both seem to have engendered a north orientation. Given the connection between Ptolemy’s Geography and his astronomical and astrological works, the Almagest and the Tetrabiblos, I also have to wonder if the cosmographical significance of the celestial north pole, so fixed in the night sky, had some significance too in the north-orientation of world maps. This north-orientation had nothing to do with the magnetic compass, which would not, of course, be introduced into the Mediterranean for a full millennium after Ptolemy.

When Ptolemy’s work was adopted as a model for regional and world mapping in the fifteenth century, geographers also generally adopted Ptolemy’s habit of placing north at the top. Not always, but generally so, and quite unrelated to the magnetic compass.

Marine Charting

It has long been suspected that the development of graphic marine maps in the Mediterranean region was connected to, or even caused by, the introduction of the magnetic compass from ancient China. Nineteenth-century map historians accordingly called them “compass charts.” Such maps have compass roses as a frequent motif:

I made this compass rose in 1996 by running an image of a compass rose from a medieval sea chart through multiple filters in PhotoShop (or whatever software I was using at the time)

I made this compass rose in 1996 by running an image of a compass rose from a medieval sea chart through multiple filters in PhotoShop (or whatever software I was using at the time)

The kicker, though, is that even with their radiating networks of rhumb lines, medieval marine maps had no orientation: they were intended to be read from all sides equally, and the names of ports and headlands were placed perpendicularly to the coastline, regardless of the coast’s direction. That is, the introduction of the compass among mariners manifestly had no effect on the orientation of marine maps.

After the Portuguese began after 1420 to sail south along the coast of Africa, they ended up modifying the marine maps of the Mediterranean Sea for the conditions of the Atlantic. In particular, this included the insertion of latitude scales, when latitude was measured by the height of the pole star/celestial pole and then by the height of the sun at noon (when due south). However, the lines running parallel to the latitude scales did not represent meridians … long story and not relevant for this post. The eventual dominance of north-orientation of marine maps, as the Portuguese practice of “plane charts” spread to the Dutch, French, and English, thus had little to do with the magnetic compass, even if mariners actively used the magnetic compass at sea.

(The reconciliation of magnetic and true north on marine maps is far too complicated for this post.)

Property Mapping

The magnetic compass is not a requirement of the instrumentation of property mapping, although it became a common element in that instrumentation in the early modern era. By and large, early modern property maps were plotted out so as to make the most efficient use of the paper (a costly resource), so that it is hard to observe any predominant orientation among them. (This would be an interesting exercise!)

Under standardized conditions—such as the organized land division of colonial New England—property lines were run with surveyor’s compasses and similar instruments. The indication of a compass rose on graphic property maps referenced the surveyor’s compass. Only in the 1790s did surveyors in the new USA seek to take magnetic variation into account and align new cities and towns to true rather than magnetic north. In this respect, the spread of true-north-orientation as standard practice seems to stem more from the rise of formal training and standards for civil engineers and surveyors than from the instrumentation.

And so on …


North orientation certainly became a common characteristic within different mapping modes in the early modern and modern eras, such that it is possible at times to say that deviance from the convention is socially and culturally significant. But, north orientation stemmed from different aspects of mapping practices, specific to each mode, and was not part of some universal standard for “maps” that has only ever existed in modern minds.