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Ed. note: This article originally appeared in the
September/October
2008 issue of Pathfinder.
In this era of GPS, homeland security and geospatial support to
disaster relief operations, the civilian sector is beginning to realize
what the military has known since World War I: for land navigation, the
geographic coordinate system using latitude and longitude is not
well-suited for referencing locations. The geospatial community,
including NGA, has established and is working to implement a simple
rectangular X, Y coordinate system for domestic location referencing,
the U.S. National Grid (USNG).
The geographic coordinate system is essential for referencing large
areas of the Earth, but for small areas, it has serious drawbacks - it
uses angular units (degrees, minutes and seconds), which are cumbersome
when expressing distance or converting coordinate values between map
scales, and the spacing of latitude and longitude varies across the
Earth, resulting in complicated calculations. USNG avoids these
problems.
For example, rather than express distance in degrees, minutes and
seconds, a gardener of a small backyard plot would more likely
construct a simple X, Y grid, using linear units such as feet or
meters. That way, the azalea hedge could be expressed as "60 feet long"
instead of "0.6 seconds of latitude from end to end."
The same principle applies to land navigation, as the Allies realized
during World War I. They abandoned geographic coordinates in favor of
X, Y coordinates for guiding artillery fire and reporting positions,
placing coordinates derived from rectangular grids on maps covering
Allied areas of operation. This method was continued throughout World
War II, but the global nature of that war made apparent the need for a
uniform, worldwide system. In 1947, efforts by the U.S. Army Map
Service and other Allied mapping organizations resulted in the
development and adoption of the Universal Transverse Mercator (UTM)
coordinate system, which uses a rectangular grid, and its associated
location reporting method, the Military Grid Reference System (MGRS).
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Implementing
the U.S. National Grid, as depicted on this map of St.
Louis, MO. will enable emergency responders to operate more
effectively. Sample map provided by Kurt Schulz.
Half a century later, the civilian sector began to grapple with the
issue of map grids for location reporting. With the rapid growth of GPS
technology in the 1990s, anyone could use a handheld GPS receiver to
quickly determine precise geographic positions. GPS soon became
essential for emergency response, disaster relief, and
search-and-rescue operations.
Unfortunately, this advance remained hampered by the geographic
coordinate system and other inadequate position referencing systems.
Street addresses offered only limited accuracy and range, and locally
produced map grids each followed their own standards and definitions.
The need for a standardized rectangular grid reference system for
civilian use became obvious.
Recognizing this need, leading members of the U.S. mapping sciences
community formed the Public XY Mapping Project in 1997. Representatives
of the National Imagery and Mapping Agency, which would become NGA,
soon became involved in the project. After considering several
possibilities, the project committee concluded that a UTM-based,
slightly modified version of MGRS would be the best choice for a
standardized, national map grid for civilian use. In 2001, the U.S.
National Grid became a standard for the interagency Federal Geographic
Data Committee (FGDC), which was established in 1990 to coordinate
geospatial data nationally. USNG is the preferred grid for applications
of the National Spatial Data Infrastructure, the FGDC's data publishing
effort.
The USNG is functionally equivalent to MGRS. In this system, the U.S.
is divided into 6°x 8° grid zones, each with a three-character
designator. These zones are further divided into 100-kilometer grid
squares, each with a two-letter identifier. A location within a
100-kilometer grid square is referenced with an alphanumeric value
composed of the grid zone designator, the grid square identifier, and
X, Y coordinates measured, in meters, from the southwest corner of the
grid square.
Currently, first responders and public safety officials have little
training or experience with grid systems for location referencing, and
many geographic information system (GIS) managers at the state and
local level are unfamiliar with the USNG. For many, the response to
Hurricane Katrina dramatically revealed the need to adopt a national
standard. Trapped residents reported their addresses, but many street
signs and house numbers were submerged or destroyed. Specialists
converted addresses to coordinates, but many responders lacked the
training and technology to relate coordinate values to actual locations.
Civilian agencies, local governments and private companies need to be
educated, persuaded and encouraged in the use of the USNG to recognize
its importance and initiate implementation under a spirit of
cooperation, which is beginning to occur. Florida and North Carolina
have recently adopted the USNG as their official standard for
search-and-rescue and other emergency operations. GIS advisory councils
in other states are also considering implementation.
Crucial to implementation is the placement of the USNG on geospatial
products and technology. The challenge of establishing the USNG in the
civilian sector presents a unique opportunity for NGA. With its years
of experience administering MGRS and UTM and its leadership role in the
geospatial community, the agency can pass along its expertise and
knowledge of grid systems to mappers in the public safety field.
NGA's Office of the Americas, North America and Homeland Security
Division, now includes the USNG on domestic geospatial intelligence
(GEOINT) graphics, and the NGA Support Team serving the Department of
Homeland Security portrays the USNG on the Ground Search Maps produced
for the Federal Emergency Management Agency's (FEMA's) Urban Search and
Rescue. The NGA Office of GEOINT Sciences, Coordinate Systems Analysis
Branch has provided useful guidance to these efforts.
The wider geospatial community is also making progress toward
implementing the USNG. The U.S. Geological Survey's National Map, its
online interactive map service, includes the USNG, as does the
Department of Transportation map of Washington, D.C. In addition,
several state and local GIS managers have caught the vision, portraying
the USNG on GIS-generated maps and providing USNG coordinates for land
parcels.
The geospatial community, including NGA and other federal agencies,
professional organizations and academic institutions, can all assist by
adopting and promoting USNG. As the public becomes more familiar with
the USNG and grid referencing, implementation will become easier.
As inclusion of the USNG on map products increases, so will acceptance
of the USNG by the civilian community. NGA is poised to help all its
customers take part in this important initiative. The work of NGA and
the geospatial community to implement the USNG will continue to improve
public safety and homeland security operations for a safer and more
secure nation.
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