Cartography Word of the Day: Meridian

The first in an irregular series exploring the discipline through its terminology

Maps not only come in graphical forms but textual forms. The best textual map of any discipline is the glossary. In the case of cartography, terms of the art are not only interesting but imbued with some history. This irregular series aims to map cartography by exploring its terms, looking at thier roots, and having a little fun with its history.

With this fixed firmly in mind, let’s explore the word meridian.

According to Webster’s New Dictionary of the English Language, 2002 edition, the word stems from Latin meridianus and thence from Middle French meridien. where the meri part refers to center in the way of a midpoint and dien from the Latin for “day”.

Literally, then, the word can be reduced to the term “mid day”, or “noon”. But the current meaning of the word represents a line on the earth’s surface, a part of the global cooridinate system of latitude and longitude.

To better understand the word, let’s go back to the time before there were time zones.

Before the advent of rail travel, when everyone used their own feet (or those of animals) to get places, time was reckoned locally. This method was based on the transit of the sun across the sky, and was called solar time. This worked well on the human scale. it meant that noon–meridien–was when the sun was straight up in your local sky. This is also the genesis of the commonly accepted for morning (A.M.–ante meridiem or before noon) and afternoon/evening (P.M.–post meridiem).

The cross sections of the earth are considered as a circle, and divided into 360 degrees. at each degree, an imaginary line is considered to run through both north and south poles and at a 90 degree angle to the Equator.
Each one of these 360 circles is a meridian of longitude.

Further divisions are used to organize and rationalize the system. A single meridian is chosen as the staring point; this is called the prime meridian and has a longitude of zero degrees. By international convention this is marked by the Royal Observatory in Greenwich, a suburb of London, in England. When we refer to degrees west and degrees east, we refer to our position relative to Greenwich. The continuation of the prime meridian on the opposite side of the globe is the basis for the International Date Line.