Words for Thought - Notes from The Glossary of Mapping Sciences

By Dr. Melissa Tolene Rura posted 01-14-2015 13:08

During the Christmas break I was part of a discussion within Sigma Xi (The Scientific Research Society) about terms of old measurement.  This got me to thinking again about how important it is that the measuring sticks we use in life and in mapping are not just assumed but also considered and questioned.  But what STOOD OUT in that discussion is how these terms change over time.  Here are a few terms to mull over:

acre  n., Meas., A unit of area in the English system of measure, defined as 10 square chains (1 chain is 4 rods or 66 feet).  It is exactly equal to 43,560 square feet or 4,840 square yards and is approximately equal to 4046.8564224 square meters.  There are 640 acres in one square mile.  Although acre may be defined otherwise in some localities, these are local definitions and the word is usually qualified as builder's acre or Block Island acre.  The English system of measures contains no legally defined unit of area.  The size of the acre therefore depends on the length of the English yard, which is legally defined.  By an ordinance of Edward I in 1303, the acre was defined as the area contained in a rectangle 40 rods long and 4 rods wide.  With the rod defined as 5.5 ulnae (yards) as defined by Edward I's iron standard for the ulna, the acre is 4840 square yards.

acre-foot  n., Meas., The volume of water required to cover one acre to a depth of one foot.  Equivalent to 43,560 cubic feet of water, it is a convenient unit for measuring the amount of water in a reservoir, the amount needed for irrigation, or the amount of runoff.  SEE ALSO acre.

Ångström  n., Meas., A unit of length equal to 10-10 meter.  Also called the Ångström unit.  Also spelled Angstrom and angstrom.  Its symbol is Å or A.  It was invented to measure wavelengths in the optical (8000 ‑ 4000 Å) part of the spectrum and below (ultraviolet and X-ray).  It is not an accepted part of the SI but is still used in spectroscopic literature.  The designation preferred by the SI for, e.g., the visible part of the spectrum would be 8000 ‑ 4000 nm (nanometers).

are n., Meas.,  A unit of area equal to 100 square meters.  The unit is used primarily in agriculture and related arts.

arpent  1. n., Fren., Meas., An old French unit of area.  The size of the arpent depends on its origin and on local custom.  The value 0.8507 acres has been used for surveys in Arkansas and Missouri.  For surveys in Louisiana, Mississippi, Alabama, and northwestern Florida, when no alternative definition for the arpent has been known, the value 0.84725 acres has been used.  The arpent was used, in the U.S.A, in surveys of land granted by the French crown.  2. n., Fren., Meas., An old French unit of distance, taken as the length of a side of a square region one arpent in area.  Its values in other units, corresponding to the values given in (1.) for area, are:

  1 arpent (0.8507 acres) =    192.500 feet or 58.674  m

  1 arpent (0.84725 acres) = 191.995 feet or 58.5198 m.

In Canada, the arpent is exactly 180 French feet, which is about 191.85 English feet. (SEE foot).

bar   1. n., Meas., A unit of pressure equal to 106 dynes per square centimeter.  Formerly called the barye.  It was first suggested by Bjerknes in 1911.  In SI units, it is 105 newton/m² or 105 Pa.  The unit is used in both meteorology and oceanography.  One standard atmosphere is 1.013250 bars.  The pressure exerted by a column of water 1 m deep is very nearly 1 decibar (1 dbar), which makes the unit convenient for oceanographers.  2. n., A long object of uniform but arbitrary cross-section and of considerable mass.  The width and depth of the solid are about the same.  If the width is considerably greater than the depth, or vice versa, the object is called a sheet.  3. n., A ridge or mound of sand, gravel, or other unconsolidated material below the level of high water, especially at the mouth of a river or estuary, or lying a short distance from and usually parallel to a beach, and which may obstruct navigation.

  n., Meas.,An old measure of length, equal to the average length of a grain of barley; the third part of an inch..

cable length  n. Meas.,120 fathoms or 720 feet.

chain  1. n., Meas., The unit of length prescribed by law for the survey of the public lands of the United States of America and equal to 66 feet or 100 links.  One acre equals 10 square chains.  The chain derives its name from the Gunter's chain, which was widely used in early surveys and had the form of a series of links connected together by rings.  2. n., Meas.,  A Gunter's chain or similar measuring device.  SEE ALSO engineer's chain; Gunter's chain; throwing the chain.

chain, nautical  n., Meas.A unit of length equal to exactly 15 feet.

chain, two-pole  n., Meas.,  A chain 33 feet long.

Committee Metre  n., Meas., The iron bar of one metre length brought to America in 1805 by Ferdinand R. Hassler, the first superintendent of the U.S. Coast Survey, for use by that survey as a standard of length.  The Committee Metre was one of sixteen such bars calibrated by the Committee on Weights and Measures in Paris in 1799 against the Prototype Metre.  It served as the standard of length for geodetic surveys in the United States of America until 1889 or 1890, when it was replaced by the National Prototype Meter.  The Committee Metre was presented by Hassler to the American Philosophical Society in Philadelphia.


This is, of course, a very shortened list.  But as I sifted through these terms this winter and again this morning and I reflected on how time and place are important in so many.  This morning is was also very poignant how involved the French are and were in the definition of many measures of mapping and often their standardization.  I know, reading "The Measure of All Things: The Seven-Year Odyssey and Hidden Error That Transformed the World" as a part of a class during my master's degree changed my perspective on measurements and the human involvement in them.  (In June 1792, French Revolution begun, Jean-Baptiste-Joseph Delambre measured north, while Pierre-François-André Méchain measured south. Their mission was to define the meter as one ten-millionth of the distance between the pole and the equator.  France's hope to define a standard that would be used “for all people, for all time.”)  

The French recognized then their need, the desire of their people for a uniformity in measurement consider the definition of arpent above.  But often in our desire to make things more alike or uniform we lose the variety and plurality that makes us strongest.  On which rock would you like to build your house a conglomerate or shale?  There are draw backs to both...

In this blog we will post terms and themes of related terms and their 
definitions that come from the The Glossary of Mapping Sciences with commentary.  In the hope that by discussing the meaning of words we come to deeper understanding and more meaningful usage.