Summer Issue 2021 - 84

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The metric acre could fill a
missing intermediate scale
between square meters and
hectares and, like the metric
ton, bridge the gap between
the imperial and metric
systems.
The United States is one of
only three countries-the others
being Myanmar and Liberia-that
have not officially adopted the metric
system as their primary means of
weights and measures. While the
Metric Conversion Act of 1975 designated
the metric system as " the
preferred system of weights and
measures for United States trade
and commerce, " it did not mandate
it, and American planners and developers
continue to use inches, feet,
and acres, while 95 percent of the
world's population uses centimeters,
meters, and hectares.
Unfortunately, the metric system
The metric system has no direct
corollary to the acre. A square meter
(at 10.76 square feet) is too small; a
hectare (at 2.47 acre) is too large. A
square metric acre is defined as 60 by
60 meters (196.9 by 196.9 ft), which
is close to the historic American
200-by-200-foot (60.96-by-60.96-m)
urban block. But it fits squarely and
accurately into the metric system.
has no direct corollary to the
imperial system's acre. The usual
conversion, and the one used in
this magazine, is a hectare. But
the hectare-which comprises 2.47
acres-is too large for most transactions
and the square meter--
which comprises 10.76 square
feet--is too small.
WILLIAM P. MACHT
A " Metric Acre " Would Integrate American
Development Practices with Global Measures
Rather than directly convert each
measurement from the imperial
system, this author argues, American
planners and developers should
mediate the transition by using close
approximations of their existing
development practices, but which
also fit precisely into the metric
system. The adoption of a metrically
accurate 60-by-60-meter metric acre
(a metric mediation analogous to
the metric ton) could form a mental
framework into which planners and
developers could more easily place
daily experiences and practices.
This could also make land use more
effective, building products less
expensive, appliances more efficient,
and housing more affordable.
History of the Imperial
System
The imperial system of measurement
was based on anthropomorphic
measurements of the king's
foot, divided into 12 segments,
and the inch, which was the width
of the thumb. The system was
convenient since every man bore
its measurement approximations.
Land measurement was based
on the mile and the acre. An
imperial mile originated from the
Roman mille passum or " thousand
paces " (left-right-left), which measured
5,000 Roman measurement
feet. Roman roads in England were
marked with milestones. Under
Queen Elizabeth I in 1593, a statute
confirmed the change from
the longer Anglo-Saxon foot to a
shorter foot that made the length
of a mile 5,280 feet, consistent
with field measurement practices.
The acre was derived from the
strip of land that a man with a
team of oxen could plow in one
day. (The word acre is based on
the Greek term agros and the
Latin term ager, meaning field.)
In 1623, English mathematician
84
URBAN LAND
SUMMER 2021
Edmund Gunter systematized
that scale for surveying land by
designing a 66-foot iron chain
of 100 links (thereby implanting
a decimal metric) that could be
carried by a surveyor and referred
to as one chain. One mile was 80
chains, or 5,280 feet. An acre was
determined to be 66 feet (one
chain) wide by 10 chains (one furlong,
a long furrow) 660 feet long
(43,560 sq ft). Its shape was long
and narrow because that was the
length that a team of oxen could
plow without stopping, and reversing
the team was laborious.
Measuring an equal-sided
square acre was more difficult
since the square root of 43,560
square feet is 208 feet 8.5 inches,
which is hardly intuitive. But 10 by
10 chains equals 660 by 660 feet
(435,600 sq ft), equaling 10 acres.
And it was that dimension-and
divisions thereof-that pioneering
new American cities adopted and
surveyed using Gunter's chain.
Englishman James Oglethorpe
designed the Savannah Wards in
1733 based on that 10-acre form,
as did Chicago in 1830 and Salt
Lake City in 1847.
In 1781, the Articles of Confederation
declared the acre the standard
unit of land measurement.
Those dimensions in a square
grid became the national system
of land measurement devised by
Thomas Jefferson to survey land
from Ohio westward. The Northwest
Ordinances of 1785 and 1787
separated the land beyond the
original 13 states into six-squaremile
gridded townships (480 by
480 chains), divided into 36 onesquare-mile
sections (80 by 80
chains equal 5,280 by 5,280 feet,
or 640 acres), which could easily
be halved, quartered, or otherwise
divided. The surveying paths on
the section lines usually turned
MACHT & COMPANY
Summer Issue 2021

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