Location, Trigonometry, and Measurement of the Sphere - Spatial Mathematics: Theory and Practice through Mapping - page 44

highly accurate. A typical coordinate might be 310,200 feet north, 88,410
feet west, Wisconsin Central Zone, NAD 83 HARN (indicating the horizontal
datum used), US Survey feet (indicating the units). In a similar fashion, many
other countries have their own reference system, such as the British National
Grid or the New Zealand Map Grid, for use in topographic mapping and
digital spatial data.
A third additional coordinate system is the Universal Transverse Mercator
(UTM) system. The US National Geospatial Intelligence Agency adopted
this grid for military use throughout the world, dividing it into 60 north-
south zones. Each zone covers a strip 6° wide in longitude so that all 360°
of the Earth could be completed. The zones are numbered consecutively
beginning with Zone 1, between 180° and 174° west longitude, progress-
ing eastward to Zone 60, between 174° and 180° east longitude. The con-
terminous US States are covered by 10 zones, from Zone 10 on the west
coast through Zone 19 on the east coast. In each UTM zone, coordinates
are measured east and north in meters as “eastings” and “northings.” Let us
take the second value first, the northing, because it is more straightforward.
This northing value is measured continuously from zero at the Equator, in
a northerly direction. Thus, a northing of 3,446,250 is exactly 3,446,250
meters, or 3,446.25 kilometers, north of the Equator. To avoid negative
numbers for locations south of the Equator, the Equator is assigned an arbi-
trary false northing value of 10,000,000 meters. Now let us consider the first
value, the easting: A central meridian through the center of each 6° zone
is assigned an easting value of 500,000 meters. Why 500,000? Again, it is
simply given a high enough value to ensure that no easting coordinate will
have a negative number. Values to the west of this central meridian are less
than 500,000; to the east, they are more than 500,000. An easting value of
529,781 is 29,781 meters, or 29.781 kilometers east of the central meridian
in that zone. Thus, a full UTM coordinate example is 391,000 meters east-
ing, 3,456,789 meters northing, UTM Zone 13. The zone is needed because
the same coordinates (such as 391,000 meters easting, 3,456,789 meters
northing) can exist in more than one zone (such as Zone 13 and Zone 14).
In Figure 2.2 , Edmonton, Alberta, Canada is designated as a point and
three different descriptions for it are given: Approximate address, latitude/
longitude, and UTM coordinates.
The fourth coordinate system that is in wide use at least in the United
States is the Public Land Survey System (PLSS). It began in eastern Ohio
with the Land Ordinance of 1785 with the opening up of the American
West, and was the primary system used to subdivide the land for sale to
homesteaders over the next century and a half. It continues to be used to
the present day. It covers about 2/3 of the country, primarily in the central
and western portion, with the exception of Texas. It is referenced off of a
series of meridians and baselines, with the land divided up into ranges and
townships of 36 square miles, and sections of one square mile. Each section