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United States National Grid

United States National Grid (USNG)

Date Issued : Approved by the Minnesota Governor's Council on Geographic Information 03/25/2009

Introduction:
This standard describes a method for presenting the United States National Grid (USNG) in cartographic products. The USNG provides an efficient way to specify location information at different levels of detail anywhere in the United States. It can increase the usefulness and interoperability of printed maps and location-based services, such as global positioning systems (GPS). It is based on a universally defined geographic coordinate and grid system.

A number of different coordinate and grid systems can be used on printed maps and computer map displays in order to describe locations. When different systems are used on different maps, however, it is difficult for people to translate between them. Eliminating the need to translate has become particularly important during emergency response situations in which people need to communicate locations quickly, clearly and confidently. Widespread use of the USNG promises to provide a fast, unambiguous, repeatable way to communicate locations.

The USNG is based on a common geographic projection and rectangular grid system (Universal Transverse Mercator). It has practical advantages over using geographic coordinates (latitude, longitude). USNG location references correlate directly to field measurements. Therefore, distances can be accurately calculated between two locations easily, and the precision of locations and measurements can be maintained consistently across the state and across the nation. This is not true with geographic coordinates.

Applicability:
Who cares about these standards?
This standard pertains to all developers, distributors, and users of map products within the State of Minnesota including government agencies, private organizations, and the general public. The USNG is of particular interest to the emergency management and response community.

When do they apply?
This standard applies when the USNG is represented on hard-copy maps, implemented in digital maps, or used for identifying and communicating locations.

When do they not apply?
This standard does not apply to actual collection or storage of geospatial data. The USNG supplements other location referencing systems, such as street addresses or latitude / longitude. It does not replace them.

Purpose of this Standard:
The purpose of this state standard is to encourage the use of the USNG on all appropriate map products in the state and to specify how the USNG should be presented on maps when it is used. The USNG is intended to improve interoperability across all national jurisdictions especially in crisis situations. It is also intended to help people use location services such as GPS in conjunction with printed maps to find and communicate location information.

Standard Requirements:
This standard implements the U.S. National Grid standard developed by the Federal Geographic Data Committee (FGDC), documented as FGDC-STD-011-2001, and included in its entirety by reference in this standard. This FGDC standard defines the specifications of the USNG and describes how the grid is to be presented on map products. It can be found at:

http://www.fgdc.gov/standards/projects/FGDC-standards-projects/usng/fgdc_std_011_2001_usng.pdf

The following are main features and specifications of the USNG:

Equivalency with MGRS. In Minnesota, USNG coordinates are identical to the Military Grid Reference System numbering scheme, the geo-coordinate standard used by NATO militaries for locating points on the earth.

Basic Numbering. USNG basic coordinate values and numbering are identical to UTM coordinate values over all areas of the United States.

Referencing Scheme. The numbering scheme used in the USNG is alphanumeric and follows these rules:

Grid Zone Designation. First, the U.S. geographic area is divided into 6-degree longitudinal zones designated by a number and 8-degree latitudinal bands designated by a letter. Thus each area is given a unique alphanumeric Grid Zone Designator (GZD).

The longitude zone numbers and latitude band letters for GZD over the United States are taken from the global scheme of MGRS.

Example: 18S - Identifies a GZD.

100,000-meter Square Identification. Each GZD 6x8 degree area is covered by a specific scheme of 100,000-meter squares where a two-letter pair identifies each square.

Example: 18SUJ &- Identifies a specific 100,000-meter square in the specified GZD.

Grid Coordinates. - A point position within the 100,000-meter square shall be given by the UTM grid coordinates in terms of its Easting (E) and Northing (N). For specific requirements or applications, the number of digits will depend on the precision desired in position referencing. In this convention, they read from left with Easting first, then Northing. An equal number of digits are always used for E and N.

Examples:
18SUJ20 - Locates a point with a precision of 10 km
18SUJ2306 - Locates a point with a precision of 1 km
18SUJ234064 - Locates a point with a precision of 100 meters
18SUJ23480647 - Locates a point with a precision of 10 meters
18SUJ2348306479 - Locates a point with a precision of 1 meter
18SUJ2348316806479498 - Locates a point with a precision of 1 millimeter

Relationship to Datums.- The standard datum for USNG coordinates is the North American Datum 1983 (NAD 83) or its international equivalent, the World Geodetic System 1984 (WGS 84).

Accuracy.- Paper maps using the USNG are expected to conform to the National Map Accuracy Standard.

Precision.- USNG provides a flexible numbering scheme to accommodate variable precision from tens of kilometers to sub-meter.

Compliance:
What constitutes compliance?
When Minnesota state agencies present the USNG on printed map products that claim conformance to this standard, they must be in compliance with FGDC-STD-011-2001 . (See page 5 of the federal standard for compliance requirements.)

County, municipal and other local governments and private organizations are encouraged to use this standard when producing similar map products.

How will compliance be measured?
Compliance is determined by conformance with FGDC-STD-011-2001. Compliance can be made easier through the development and implementation of organizational guidelines, training, and requirements for map products that implement the USNG.

Notes:
When map products are designed or updated, the USNG should be considered as a location reference aid consistent with map products in other jurisdictions employing the same standard. Use of this standard by state and local governments, as well as by private companies, will result in maps that are interoperable. Since the USNG is a federal standard, locally produced maps employing this standard will be more effective for use by federal resources, most notably in disaster response events. The USNG should be further considered for defining map extents and index maps for map series, as well as grid cells for depicting field observations at varying resolutions, such as damage assessment and disaster recovery status.

References and Sources of More Information:

US National Map Accuracy Standards http://rockyweb.cr.usgs.gov/nmpstds/nmas647.html