In the January–February
issue, the author discussed how military logistics management
often do not provide visibility of equipment in shipment. In
this article, he shows how the basic concepts of latitude and
longitude are helping to solve this problem.
Although military logistics management systems still do not
provide total visibility of items in shipment, the Department
of Defense has made tremendous progress in its ability to
locate items in transit.
checks coordinates on a map while on patrol near
the Syrian border in Iraq.
In 1492, when “Columbus sailed the ocean blue,” the use of geometry
and observation of the position of the Sun and the stars were the primary methods
of navigation. Like other learned people of his day, Columbus believed the Earth
was round. This meant that he could use the geometry associated with a circle
(360 degrees) and the Sun’s position on the horizon to navigate. Although
he sailed over 500 years ago, Columbus was able to estimate his latitude through
the use of a quadrant and navigational charts. Unfortunately, since the chronometer
had not yet been invented, the same could not be said for his longitude. So,
during his first voyage to the new world, Columbus and his sailors could only
guess how many miles they were from home once they left the familiar waters
around the Canary Islands and sailed westward.
Before the global positioning system (GPS) was invented, the sextant was the
primary tool used for navigation. It measures the degree of angle between the
horizon and the noonday sun. By comparing the angle to published tables, the
user of the sextant can determine latitude. Latitude has been a lifeline for
mariners for several hundred years.
After the mutiny aboard his vessel, the H.M.S. Bounty, Captain William Bligh
was placed aboard a lifeboat, and, in one of the greatest feats of navigation
ever accomplished, he and his 18 crewmembers sailed the open boat 3,600 miles
to the Dutch colony of Timor using a sextant as their primary navigational tool.
Early navigation at sea was a problem because of the difficulty in calculating
longitudinal position. Although navigators could determine their latitude by
measuring the Sun’s angle at noon, they had no means of estimating longitude.
They lacked a portable method of determining time of day that would function
on a ship. The clocks available at the time were pendulum clocks, which were
useless on a rolling ship at sea. In 1763, John Harrison, a carpenter from
Yorkshire, England, perfected a clock (chronometer) that was not affected by
the motion of a ship.
Once the chronometer was invented, a mariner had to know only the time of day
at his location and the time of day in Greenwich, England, to determine his longitude.
At the Equator, if Greenwich time was 1200 and local time was 1600, a mariner
knew that he was 4,200 miles west of Greenwich, England (each hour representing
about 1,050 miles, or 15 degrees of longitude).
The concepts of latitude and longitude, premised on the fact that the Earth is
nearly round and has a magnetic north, are not only one of the oldest means of
identifying location but also one of the best.
is shown as horizontal lines that are parallel to
the equator, which is used as one of two navigational
reference points. It is designated as 0 degrees latitude.
Longitude is shown as vertical lines that are east
or west of the prime meridian, the other reference
point, which is designated as 0 degrees longitude.
World Geodetic System
Emerging technology holds the promise to simplify location identification. Satellite-based
GPSs and digitized maps frequently express physical locations using the conventions
of the World Geodetic System (WGS), which was developed in 1960. Latitude and
longitude are essential components of the GPS, so it is important to understand
Latitude. The Earth has a circumference of about 25,000 miles at the
Equator and a slightly smaller circumference around the poles. Since the Earth
round, it can be divided into 360 degrees. Therefore, we can express location
by using the angles of arc between two reference points. Latitudes are horizontal
lines that are parallel to the Equator, which is used as one of two reference
points; it is designated as 0 degrees latitude.
In the WGS, minutes and seconds are not expressions of time but the amount
of arc in the circular Earth. There are 60 minutes (of arc) in a degree and
(of arc) in a minute. Therefore, each degree of latitude represents about
69 miles (the Earth’s 25,000-mile circumference divided by 360 degrees
equals 69 miles). A location with latitude of 45 degrees north is halfway
the Equator (0 degrees latitude) and the North Pole (90 degrees latitude
north). A location with latitude of 45 degrees south is halfway between the
degrees latitude) and the South Pole (90 degrees latitude south). In the
WGS, it is not possible to exceed 90 degrees latitude.
Longitude. Longitude lines (also called meridians) are vertical lines
that connect at the poles. Longitude represents location as an angle between
a line running
north and south through Greenwich, England (called the Prime Meridian), and a
vertical location point. The Prime Meridian is the other reference point; it
is designated as 0 degrees longitude. Moving west fromthe Prime Meridian, one
would pass the east coast of the United States, the west coast, and Hawaii to
a maximum longitude of 180 degrees west. This is the location of the international
dateline, which is on the opposite side of the world from the Prime Meridian.
Heading east from the Prime Meridian, one would pass through France and Russia
to a maximum longitude of 180 degrees east. This would again be the international
Converting angles of arc into distance for longitude is much different than for
latitude. While lines of latitude are parallel and remain at a constant distance
from one another, lines of longitude converge at the poles. The distance between
degrees of longitude at the Equator is 69 miles; the distance between degrees
of longitude at either of the poles is 0. Typically, the latitude and longitude
grid lines shown on world maps are 15 degrees apart. Locations are pinpointed
using degrees, minutes, and seconds of latitude and longitude. The latitude and
longitude for San Diego, California, for example, are latitude 32 degrees, 51
minutes, and 9.36 seconds north and longitude 117 degrees, 6 minutes, and 36
GPSs are helping to transform logistics. Twenty-four solar-powered satellites
that are 12,000 miles above the Earth serve as the foundation of the GPS. To
determine their current location, military personnel can use GPS receivers
to retrieve radio signals from the satellites. If they are able to receive
from three different satellites, the GPS receiver can display location to within
plus or minus 10 meters. If the GPS receiver can pick up signals from four
or more of the satellites, military users also can determine altitude.
With GPS information—expressed in latitude and longitude and accurate to
within 100 feet or better—deployed forces can easily determine their
current locations. These could be established sites such as aerial ports
shallow-draft seaports, highway intersections, container consolidation points,
or supply points. Deployed forces also can use a GPS to determine temporary
sites, such as supply storage areas hastily assembled in forests or deserts,
helicopter landing zones, tactical assembly areas, container-handling areas,
and ammunition transfer points. Once this location information is loaded
into a computer network, joint logisticians worldwide can use a variety of
programs to view the locations and surrounding areas on digitized maps. For
example, if a Soldier located in a forest on the island of Sumatra needs
provides the latitude and longitude of his location to a logistician in Australia,
the logistician can access a digitized map database, analyze the surrounding
area, determine the best route of resupply, and program a Joint Precision
Airdrop System, loaded with ammunition, to land within 100 feet of the desired
With the dramatic advancements that have been made in GPS
technology, telecommunications, automatic identification
technology, data processing, and advanced software
systems such as those that digitize maps, photographs, and images, there soon
will be no need to truncate word-related data fields or encode location data
for the Joint Operations Planning and Execution System, the Global Transportation
Network, or the Defense Transportation Regulation. Since current computers
and telecommunications systems can readily store, process,
and transmit a tremendous
amount of data, it is no longer necessary to encode location information. Whenever
possible, the Department of Defense should express locations as mailing addresses
(currently used in direction-finding software such as MapQuest) and cite latitude
and longitude. Because of the enormous quantity of logistics data that must
be processed to attain asset visibility of items in shipment, military shipment
labels and transportation control movement documents should be redesigned
to minimize the number of data elements that must be captured
Locating items in shipment and determining their final destinations is complex,
advancements in technology are significantly improving the process. Many streets
in countries around the world will remain unnamed; however, modern technology
will enable us at least to determine the latitudes and longitudes of equipment
Lieutenant Colonel James C. Bates, USA (Ret.),
works for Alion Science and Technology and serves as a sustainment
planner for the U.S. Joint Forces Command, Standing Joint Force
Headquarters (Standards and Training), at Norfolk Naval Base,
Virginia. He is a Certified Professional Logistician and
a graduate of the Army Command and General Staff College and
holds an M.B.A. degree from the University of Hawaii. He can
be contacted by email at James.Bates@jfcom.mil.