July - September 2005
The objective of this U.S. National Grid standard is to create a more interoperable environment for developing location-based services within the United States and to increase the interoperability of location services appliances with printed map products by establishing a nationally consistent grid reference system as the preferred grid for NSDI applications. The U.S. National Grid is based on universally-defined coordinate and grid systems and can, therefore, be easily extended for use world-wide as a universal grid reference system.
A consistent system is important because people cannot easily convert between multiple reference systems without the aid of location services appliances, calculators, or conversion tables. DHS has proposed that the United States National Grid (USNG) be used to increase the interoperability of location services appliances with printed map products by providing a nationally consistent grid reference system.
USNG relies on the familiar Universal Transverse Mercator (UTM) coordinate system and is applied not only in the United States but also worldwide. USNG is a nonproprietary alphanumeric referencing system derived from the Military Grid Reference System (MGRS). Many GPS receivers, from recreational to survey-grade instruments, support and report positional information in an MGRS/USNG format. ArcGIS 9.1 includes grid and graticule support for map layouts. The Esri Military Analyst extension supports MGRS with a dynamic coordinate conversion and provides batch conversion of data from decimal degrees to MGRS coordinates in addition to degrees, minutes, seconds (DMS) and UTM. This article introduces USNG to both casual and experienced GIS users by taking the reader on a virtual tour of the available resources for learning about USNG. It is organized as a series of stops or waypoints that are numbered from 1 through 7.
Waypoint 1The Federal Geographic Data Committee (FGDC) develops policies, standards, and procedures that enable organizations to cooperatively produce and share geographic data. This interagency committee is composed of representatives from many federal agencies. FGDC, in cooperation with state, local and tribal government organizations, the academic community, and the private sector, is developing the National Spatial Data Infrastructure (NSDI). Positional reporting and spatial accuracy are necessary when using and sharing spatial information. FGDC is a key player in the development and deployment of positional standards in government, academia, and industry. USNG provides a standard method for plotting and reporting positions across the United States.
Visit the FGDC home page (www.fgdc.gov) and look at the bottom of the page. The line immediately below the FGDC street address reads USNG: 18STJ94731361. The alphanumeric sequence, 18STJ94731361, is the FGDC's USNG address. Clicking on this link displays the location of FGDC's headquarters in the National Map Viewer. This ArcIMS-powered Web site provides a framework for geographic knowledge and gives the public access to high-quality geospatial data and information from multiple partners. Return to the FGDC home page.
Click on the USNG link at the bottom of the page to go to FGDC's USNG site and bookmark it. It contains links to the FGDC USNG standard, information on reading a geoaddress, articles, a link to The National Map portal, and other resource sites.
Waypoint 2Type www.xyproject.org to go to The Public XY Mapping Project Web site. Formed by a group of concerned citizens in 1997, The Public XY Mapping Project is a nonprofit science and education corporation dedicated to the development and implementation of spatial addressing in the United States. Spatial addresses complement conventional one-dimensional street addresses. Two-dimensional addresses can provide location information during a disaster when signs or streets are destroyed or for sites that are removed from a road network.
One of The Public XY Mapping Project's goals is to increase public awareness of the need for consistent addressing and develop and recommend FGDC/NSDI standards for a national system. USNG standards were proposed in 2000 and adopted in 2002. Since then, the project has focused on training and implementation activities.
Click on the link United States National Grid for Spatial Addressing to view a document written by N.G. "Tom" Terry Jr., The Public XY Project executive director. "A Proposal for a National Spatial Data Infrastructure Standards Project" introduces USNG and explains how it is related to the familiar Universal Transverse Mercator (UTM) coordinate system. UTM zones are six degrees wide. With USNG, these UTM zones are further subdivided into eight-degree latitude slices called Grid Zone Designations (GZDs). This article discusses the concept of address precision. Print or save this document for future reference.
Waypoint 3Return to the FGDC USNG page and click on the USNG Coordinate link to read an article written by Terry that appeared in Professional Surveyor magazine in October 2004. "The United States National Grid" provides more information on GZDs, 100,000-meter-square identification, and grid coordinates at various scales. Terry discusses numeric precision, the power of truncation, and string concatenation/presentation. This article also introduces the practice of "read right, then up" when locating a USNG address on a map. Save or print this comprehensive article.
Waypoint 4Return to the FGDC USNG page and click on "GeoaddressWhere is It?" This article, also by Terry, appeared in Professional Surveyor magazine in November 2004. It tells how USNG addressing is used to report, map, and respond to public safety emergencies in the Washington, D.C., area. It discusses the importance of integrating digital positional devices, emergency communications, digital framework data, and paper maps. This article provides a realistic look into the future of coordinate-based emergency response.
Continued on page 2