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This is an old revision of this page, as edited by Procyon28 (talk | contribs) at 21:06, 19 April 2019 (Add link to Joseph Elfelt's documentation for GISsurfer, including "Why are USNG coordinates important?"). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

Geodesy
Fundamentals
Concepts
Technologies
Standards (history)
NGVD 29 Sea Level Datum 1929
OSGB36 Ordnance Survey Great Britain 1936
SK-42 Systema Koordinat 1942 goda
ED50 European Datum 1950
SAD69 South American Datum 1969
GRS 80 Geodetic Reference System 1980
ISO 6709 Geographic point coord. 1983
NAD 83 North American Datum 1983
WGS 84 World Geodetic System 1984
NAVD 88 N. American Vertical Datum 1988
ETRS89 European Terrestrial Ref. Sys. 1989
GCJ-02 Chinese obfuscated datum 2002
Geo URI Internet link to a point 2010

The United States National Grid (USNG) is a multi-purpose location system of grid references used in the United States. It provides a nationally consistent "language of location", optimized for local applications, in a compact, user friendly format. It is similar in design to the national grid reference systems used in other countries. The USNG was adopted as a national standard by the US Federal Geographic Data Committee (FGDC) in 2001.

Overview

While latitude and longitude are well suited to describing locations over large areas of the Earth's surface, most practical land navigation situations occur within much smaller, local areas. As such, they are often better served by a local Cartesian coordinate system, in which the coordinates represent actual distance units on the ground, using the same units of measurement from two perpendicular coordinate axes.[1] This can improve human comprehension by providing reference of scale, as well as making actual distance computations more efficient.

Paper maps often are published with overlaid rectangular (as opposed to latitude/longitude) grids to provide a reference to identify locations. However, these grids, if non-standard or proprietary (such as common "bingo" grids with references such as "B-4"), are typically not interoperable with each other, nor can they usually be used with GPS.

The goal of the USNG is to provide a uniform, nationally-consistent rectangular grid system that is interoperable across local-area maps at different scales, as well as with GPS and other location based systems. It is intended to provide a frame of reference for describing and communicating locations that is easier to use than latitude/longitude for many practical applications, works across jurisdictional boundaries, and is simple to learn, teach, and use. It is also designed to be both flexible and scalable so that location references are as compact and concise as possible.

The USNG is intended to supplement -- not to replace -- other location systems such as street addresses. It can be applied to printed maps and to computer mapping and other (GIS) applications. It has found increasing acceptance especially in emergency management, search and rescue, and other public safety applications; yet, its utility is by no means limited to those fields.

Description: How the USNG Works

The USNG is an alpha-numeric reference system that overlays the UTM coordinate system.  A USNG spatial address is broken down into three parts, each of which follows a read-right-then-up paradigm familiar with other "X, Y" coordinates:

  • Grid Zone Designation; for a world-wide unique address. This consists of up to 2 digits (6-degree longitude UTM zone) for West to East followed by a letter (8-degree latitude band) from South to North; for example, "15T". [2]
  • 100,000-meter Square Identification; for regional areas. This consists of two letters, the first West to East, the second South to North; for example "EG". [2]
  • Grid Coordinates; for local areas. [Explain! Grid coordinates measured in 10,000s, 1000s, 100s, and 10s of meters up to the required level of precision. This could be a sentence after the list (and possibly below the following graphic), but the list should make some further reference to the fact that these numbers are actual distances. - RCB] [Agree - thanks! - BLH]

Reference index map (CONUS) showing first two of these. [2]

[ Add info here w/ graphics from or similar to basic description resources ->> [3] [4] [5] + other FGDC information sheets 1-4 [6] [7] [8] [9] and/or other existing training slides ]; mention...

  - refers to square at LL corner <==> truncate; no rounding (this is a good thing) [10]

- scalable to resolve ambiguity

  - truncatable to provide needed precision only (use existing size examples)

  ...typically 10m & 100m most frequent, but any can be used.

  ...succinct:  many substrings become valid references, unlike lat/lon (examples)

History

Rectangular, distance-based (Cartesian) coordinate systems have long been recognized for their practical utility for land measurement and geolocation over local areas. In the United States, the Public Land Survey System (PLSS), created in 1785 to survey land newly ceded to the United States, introduced a rectangular coordinate system to improve on the earlier metes-and-bounds survey basis used earlier in the original colonies. In the first half of the 20th Century, State Plane Coordinate Systems (SPCS) brought the simplicity and convenience of Cartesian coordinates to state-level areas, providing high accuracy (low distortion) survey-grade coordinates for use primarily by state and local governments. (Both of these planar systems remain in use today for specialized purposes.)

Internationally, during the period between World Wars I and II, several European nations mapped their territory with national-scale grid systems optimized for the geography of each country, such as the Ordnance Survey National Grid (British National Grid). Near the end of World War II, the Universal Transverse Mercator (UTM) coordinate system extended this grid concept around the globe, dividing it into 60 zones of 6 degrees longitude each. Circa 1949, the US further refined UTM for ease of use (and combined it with the Universal Polar Stereographic system covering polar areas) to create the Military Grid Reference System (MGRS), which remains the geocoordinate standard used across the militaries of NATO counties.

In the 1990s, a US grass-roots citizen effort led to the Public X-Y Mapping Project [11] [12], a not-for-profit organization created specifically to promote the acceptance of a national grid for the United States.[13] The Public XY Mapping Project developed the idea, conducting informal tests and surveys to determine which coordinate reference system best met the requirements of national consistency and ease of human use. Based on its findings, a standard based on the MGRS was adopted and brought to the Federal Geographic Data Committee (FGDC) in 1998. After an iterative review process and public comment period, the USNG was adopted by the FGDC as standard FGDC-STD-011-2001 in December 2001.[13]

Since then, the USNG has seen gradual but steadily increasing adoption both in formal standards and in practical use and applications, in public safety and in other fields.

Advantages Over Latitude/Longitude

Users encountering the USNG (or similar grid reference systems) sometimes question why they are used instead of latitude and longitude coordinates, with which they may be more familiar. Proponents note that, in contrast to latitude and longitude coordinates, the USNG provides:

  • Coordinate units that represent actual distances on the ground
  • Equal distance units in both east-west and north-south directions
  • An intuitive sense of scale and distance, across a local area
  • Simpler distance calculation (by Pythagorean Theorem, rather than spherical trigonometry)
  • A single unambiguous representation instead of the three (3) formats (for latitude and longitude), each in widespread use:
    • degrees-minutes-seconds (DMS) [examples]
    • degrees-minutes-decimal minutes (DMM or DDM)
    • decimal degrees (DDD or DD)

(This ambiguity can lead to confusion with potentially serious consequences, particularly in emergency situations [14] [15]).

  • References comprising only alphanumeric characters (letters and positive numbers). (Spaces have no significance but are allowed at certain places for readability.)
  • No negative numbers, + - N S E W <degree-sign> <minute-sign> <second-sign> [or different font sizes for principal digits as sometimes needed with all-numeric UTM]
  • A "read right then up" convention of familiar XY Cartesian coordinates.
  • An explicit convention for shortening references (at two levels) when the local or regional area is already unambiguously known.
  • A reference to a definite grid square with variable, explicit precision (size), rather than to a point with (usually) unspecified precision implicit in number of decimal places.

All of the above lead to USNG references being typically very succinct and compact, with flexibility to convey precise location information in a short sequence of characters that is easily relayed in writing or by voice.

Limitations and Tradeoffs

As with any projection that seeks to represent the curved Earth as a flat surface, distortions and tradeoffs will inevitably occur. The USNG attempts to balance and minimize these, consistent with making the grid as useful as possible for its intended purpose of efficiently communicating practical locations. Since the UTM (the basis for USNG) is not a single projection, but rather a set of 6-degree longitudinal zones, there will necessarily be a local discontinuity along each of the 'seam' meridians between zones. However, every point continues to have a well-defined, unique geoaddress, and there are established conventions to minimize confusion near zone intersections. [cite] The six-degree zone width of UTM strikes a balance between the frequency of these discontinuities versus distortion of scale, which would increase unacceptably if the zones were made wider. (UTM further uses a 0.9996 scale factor at the central meridian, growing to 1.0000 at two meridians offset from the center, and increasing toward the zone boundaries, so as to minimize the overall effect of scale distortion across the zone breadth.) The USNG is not intended for surveying, for which a higher-precision (lower-distortion) coordinate system such as SPCS would be more appropriate. Also, since USNG north-south grid lines are (by design) a fixed distance from the zone central meridian, only the central meridian itself will be aligned with "true north". Other grid lines establish a local "grid north", which will differ from true north by a small amount. The amount of this deviation, which is indicated on USGS topographic maps, is typically much less than the magnetic declination )between true north and magnetic north), and is small enough that it can be disregarded for most land navigation situations.

Adoption and Current Applications

Standards

Since its adoption as a national standard in 2001, the USNG has itself been incorporated into standards and operating procedures of other organizations:

  • In 2011, the US Government's National Search and Rescue Committee (NSARC) released Version 1.0 of the Land Search and Rescue Addendum to the National Search and Rescue Supplement to the International Aeronautical and Maritime Search and Rescue Manual. This document specifies the US National Grid as the standard coordinate reference system to be used for all land-based search and rescue (SAR) activities in the US. [16]
  • In 2015, the Federal Emergency Management Agency (FEMA) issued FEMA Directive 092-5, "Use of the United States National Grid (USNG)", whose stated purpose is "...to require use of the USNG as FEMA’s standard geographic reference system across all preparedness, mitigation, response, and recovery activities as well as land-based and land-air operations and to provide instruction for effective implementation." [17]
  • A significant number of state and local Emergency Management agencies have also adopted the USNG for their operations. [refs]
  • Other organizations including the National Fire Protection Association (NFPA) [18] and the Society of Automotive Engineers (SAE) [19] have incorporated the USNG into specific standards issued by those organizations. [ JCS document?[20] NIMS/ICS. State/county/municipal EM plans. Other... ]

Gridded Maps

existing/previous commercial maps have rectangular grids, but proprietary/nonstandard and not GPS interoperable

gridded maps (e.g., USGS topo maps, custom printing, apps, GISSurfer, MilGPS, Alexis USA (out of print?)

  • Grids on maps serve (at least) 3 purposes simultaneously...
    • Location (reference)
    • Scale (provides distance scale across the map)
    • Orientation (supplants N arrow)

Software Applications

  • USNGAPP.org, FindMeSAR.com, YourLo.ca/tion ('you are here' as coordinate display)
  • GISSurfer, MilGPS, MissionManager, others... (mapping applications)
  • The National Map (USGS); other USGS & NOAA/NGS apps

Search and Rescue (SAR)

  • (large topic- HELP!; subtopics - NASAR materials (INTSAR [21] and/or FUNSAR [22] books)) (also reference direct quote from NASAR that they are moving their training etc. to USNG)
  • NAPSG SAR USNG training [23]
  • NSARC matrix (...see SAR training at USNGIC)
  • hasty maps made easily
  • search planning, areas
  • record and report locations of searchers and/or items/clues found
  • [...other?]

Emergency Location Markers (ELMs)

<picture(s)!!>

[copied from SharedGeo; get permission or reword]-->"Since 2009, the Minnesota based nonprofit SharedGeo has been involved in research to determine the optimum way to create a marker for hiking and outdoor recreation trails and other rural scenarios where there is a need to denote a location for an emergency response.  This effort has been in response to two significant problems that plague virtually all existing approaches:

  1. Current markers of this type are jurisdictionally unique and consequently do not facilitate understanding or coordination if response resources must  be brought in from outside a region for an event like a wildfire, and
  2. Current marker systems do not work with GPS.

SharedGeo determined that both these problems can be solved by using a sign design that leverages the USNG and which conforms to various national and international display standards.  The result of this marker design effort, now known as a USNG Emergency Location Marker (ELM), is shown <graphic>.  Because this sign style provides for the report of an emergency location based on a GPS coordinate system (USNG), response efforts are significantly enhanced."[24]

Cobb County (GA)[25]

Minnesota [26], Iowa, Hawaii, others

Lake County (MN) ELM brochure [27] Cook County video [28]

Florida and other trails [USNG Florida references]

other examples (3M article [29], news articles, Eagle Scout project(s))[30]

Emergency Management

Much of the original impetus for USNG came from the field of Emergency Management. A need was seen for... [following]

- revisit FEMA Directive 092-5; 'whole community' ; all aspects [17]

- common operating picture [reference document on COP] [31]

- (rapid) situational awareness (...see DHS/FEMA training video [32] for good ways to describe this) S/A [33] or prescripted missions [34]

- NRF / NIMS / ICS (ICS-209 has entry for USNG specifically)

- list other 'early adopter' agencies/teams using right now

- contrast with Katrina issues, etc. [several good references on this]

- responders may not be familiar with local area

- street signs and/or landmarks may be gone

- Delta State Hurricane Harvey response maps [35]

- Grid based risk assessment (Talbot Brooks Delta State) & USNG as an analysis tool [36]
- NWS EDD?

- NAPSG Situational Awareness Viewer; Mission Manager

First Responders

- Al Studt fire/rescue-centric articles: FFCA article [37] Easy Geolocation [38]

- self-location apps exist (USNGapp, FindMeSAR)

- communication to PSAP (call takers)

- communication to responders (dispatch) (maybe e.g., Al's photo of 'rip/run' sheet w/ 100m coords?)

- high percentage (cite, per Al) of incidents happen away from street addresses

- local control, so adoption uneven; cite % using various methods (street address / intersection only ? proprietary grid (like ADC) ? lat/lon ? )

- (911 location horror stories in notes? Shannell Anderson / Prince / beach drowning / other car in river (...and many others))

- OTHER - BELOW

- apps, GIS vendors [39]

- (see many other citations on hub sites)

- training availability

- training -- see also GISSurfer (in Description above?) [40]

- SharedGeo and other groups

[41]
...and others [42] [43] [44]

Recreation, travel, and everyday use

Although much of the attention and application of the USNG has centered on important emergency management, response and other public safety aspects, its utility extends well beyond these fields.

Future Direction and Initiatives

The USNG has seen steady but gradually increasing adoption and use since the standard was officially approved in 2001. Formal adoption by other standards bodies has taken place, while practical adoption in actual use has been more uneven in achieving its full potential. In 2018, the USNG Institute (UGNGI) was established "to study and report on USNG implementation efforts taking place across the United States" [45], as was a USNG Implementation Working Group (USNG IWG) to help assist and coordinate implementation efforts.

Further adoption of USNG for public safety and the Emergency Location Marker system may depend in part on greater coordination of USNG adoption at Public Safety Answering Points (PSAPs, or 911 centers), in their procedures and Computer-Aided-Dispatch systems. Currently such implementations, being generally under local control, have been more fragmented than some national adoption initiatives.

Proponents of the USNG envision many other ways in which it could play roles in improving safety, convenience, and quality of life. Existing maps and mapping applications of all types could be overlaid with the USNG to provide a common frame of reference.

- USNG grid references could become commonplace, just as URLs have... navigation systems,

- recreation, travel tourism & trip planning, general use business cards, directories, travel, hiking, biking,

See also

References

  1. ^ Carnes, John (2002). UTM: Using your GPS with the Universal Transverse Mercator Map Coordinate System. MapTools. ISBN 0-9710901-0-6.
  2. ^ a b c National Geospatial-Intelligence Agency. "US National Grid Index Map" (PDF). FGDC. Retrieved 4 March 2019. {{cite web}}: Cite has empty unknown parameter: |dead-url= (help)
  3. ^ Federal Geographic Data Committee. "How to Read a United States National Grid (USNG) Spatial Address". FGDC. Retrieved 2 March 2019. {{cite web}}: Cite has empty unknown parameter: |dead-url= (help)
  4. ^ National Geospatial-Intelligence Agency. "How to Read US National Grid (USNG) Coordinates" (PDF). NGA. {{cite web}}: Cite has empty unknown parameter: |dead-url= (help)
  5. ^ MapTools. "A Quick Guide to Using USNG Coordinates". {{cite web}}: Cite has empty unknown parameter: |dead-url= (help)
  6. ^ Federal Geographic Data Committee. "US National Grid: Read Right Then Up [FGDC USNG Info Sheet 1]" (PDF). {{cite web}}: Cite has empty unknown parameter: |dead-url= (help)
  7. ^ Federal Geographic Data Committee (2 April 2008). "USNG Coordinates: World-Wide Context [FGDC USNG Info Sheet 2]" (PDF). Retrieved 4 March 2019. {{cite web}}: Cite has empty unknown parameter: |dead-url= (help)
  8. ^ Federal Geographic Data Committee (2 April 2008). "Reading US National Grid (USNG) Coordinates: Using a Coordinate Scale [FGDC USNG Info Sheet 3]" (PDF). FGDC. Retrieved 4 March 2019. {{cite web}}: Cite has empty unknown parameter: |dead-url= (help)
  9. ^ Federal Geographic Data Committee. "The US National Grid: A Simple and Powerful Geospatial Tool [FGDC USNG Info Sheet 4]" (PDF). FGDC. Retrieved 2 March 2019. {{cite web}}: Cite has empty unknown parameter: |dead-url= (help)
  10. ^ Cavell, J. Anthony. "A Guide to using the USNG", The American Surveyor, 2005. Retrieved on 14 September 2012.
  11. ^ Terry, Tom. "The United States National Grid (Article 1 of 2)" (PDF). Professional Surveyor Magazine, October 2004. Retrieved 2 March 2019. {{cite web}}: Cite has empty unknown parameter: |dead-url= (help)
  12. ^ Terry, Tom. "Geoaddress: Where Is It? (USNG Article 2 of 2)" (PDF). Professional Surveyor Magazine, November 2004. Retrieved 2 March 2019. {{cite web}}: Cite has empty unknown parameter: |dead-url= (help)
  13. ^ a b Federal Geographic Data Committee (December 2001). "United States National Grid Standard (FGDC-STD-011-2001) (1 MB)" (PDF). FGDC. {{cite web}}: Cite has empty unknown parameter: |dead-url= (help)
  14. ^ Flaherty, Mary Pat; Johnson, Jenna (23 August 2009). "Md. Medical Helicopter Faced Problems In Air And On Ground Before Fatal Crash". The Washington Post. Retrieved 4 March 2019. Baltimore had provided the coordinates as raw numbers, without specifying that they were in...degrees, minutes and seconds: 38 52 17, -76 52 26. ... Prince George's dispatchers and others mapped the coordinates differently, rendering them as decimal degrees...: 38.5217, -76.5226. Viewed that way, the numbers plotted to the coastline in Calvert County, 40 miles southeast of where Trooper 2 last was flying -- and searchers from several agencies tracked over Calvert in one of the night's misguided hunts.
  15. ^ WOOD-TV8 (Grand Rapids, MI) (5 January 2018). "Software update sends Aero Med pilot to wrong scene" (video)". YouTube. Retrieved 15 April 2019. It had to do with...the coordinates being in a different format. {{cite web}}: Cite has empty unknown parameter: |dead-url= (help)CS1 maint: numeric names: authors list (link)
  16. ^ EPC Updates (1 March 2012). "NSARC Designates USNG as the Land SAR Coordinate System". EPC Updates (St. Paul MN). Retrieved 2 March 2019. {{cite web}}: Cite has empty unknown parameter: |dead-url= (help)
  17. ^ a b Federal Emergency Management Agency (FEMA) (15 October 2015). ""FEMA Directive 092-5 - Use of the United States National Grid (USNG)"" (PDF). NAPSG. Retrieved 2 March 2019. {{cite web}}: Cite has empty unknown parameter: |dead-url= (help)
  18. ^ USNG Information Center (SharedGeo). "USNG Directives (Operational Directives and Standards)". USNG Information Center. Retrieved 3 March 2019. {{cite web}}: Cite has empty unknown parameter: |dead-url= (help)
  19. ^ SAE International. "The US National Grid Standard SAE1002". Retrieved 10 March 2019. {{cite web}}: Cite has empty unknown parameter: |dead-url= (help)
  20. ^ Department of Defense (14 May 2015). "Chairman of the Joint Chiefs of Staff Instruction (CJCSI) 3900.01D: Position (Point and Area) Reference Procedures, 14 May 2015" (PDF). jcs.mil. pp. This document provides guidance to the Armed Forces on how to reference positions. Paragraph 4.a.(2) addresses the role of the FGDC’s USNG standard for the Armed Forces in support of homeland security and homeland defense. Retrieved 5 April 2019. {{cite web}}: Cite has empty unknown parameter: |dead-url= (help)
  21. ^ Martin, Eric; et al. (2008). Introduction to Search and Rescue (2nd Edition). National Association for Search and Rescue (NASAR). p. 70. {{cite book}}: Explicit use of et al. in: |last2= (help)
  22. ^ Cooper, Donald; et al. (2005). Fundamentals of Search and Rescue. Jones and Bartlett Publishers; Sudbury, MA: National Association for Search and Rescue (NASAR). pp. 146–148. ISBN 0-7637-4807-2. {{cite book}}: Explicit use of et al. in: |last2= (help)
  23. ^ National Association for Public Safety GIS (NAPSG). "Applying USNG for Search and Rescue (Virtual Training)". Retrieved 15 April 2019. {{cite web}}: Cite has empty unknown parameter: |dead-url= (help)
  24. ^ USNG Information Center. "ELM (Emergency Location Marker) System". USNG Information Center. Retrieved 2 March 2019. {{cite web}}: Cite has empty unknown parameter: |dead-url= (help)
  25. ^ "Cobb County (GA) expands trail marker program (video)". YouTube. Retrieved 2 March 2019. {{cite web}}: Cite has empty unknown parameter: |dead-url= (help)
  26. ^ Ojeda-Zapata, Julio (5 November 2015). "Minnesota Marker Signs Might Look Funny - Until You're Lost and Need One". Twin Cities Pioneer Press. Retrieved 4 March 2019.
  27. ^ Lake County (MN) Emergency Management (2013). "US National Grid Trail Markers / Arrowhead Region, MN [brochure]" (PDF). USNG Center. Retrieved 10 March 2019. {{cite web}}: Cite has empty unknown parameter: |dead-url= (help)
  28. ^ Cook County (MN) (7 June 2016). "US National Grid Emergency Location Markers". YouTube. Retrieved 15 April 2019. {{cite web}}: Cite has empty unknown parameter: |dead-url= (help)
  29. ^ Casement, Sue. "A Skier Lost in Minnesota's Arrowhead Looks Up and Sees This: Hope". 3M. Retrieved 10 March 2019. {{cite web}}: Cite has empty unknown parameter: |dead-url= (help)
  30. ^ Robbins, Benjamin (2015). "Eagle Scout Service Project: Hawaii Volcanoes National Park". Retrieved 10 March 2019. {{cite web}}: Cite has empty unknown parameter: |dead-url= (help)
  31. ^ Gregory, Mike (22 March 2008). "Situational Awareness and Common Operating Picture in Emergency Management" (PDF). pp. 54–58. Retrieved 9 April 2019. {{cite web}}: Cite has empty unknown parameter: |dead-url= (help)
  32. ^ Federal Emergency Management Agency (FEMA). "FEMA USNG Training Video". YouTube. Retrieved 4 March 2019. {{cite web}}: Cite has empty unknown parameter: |dead-url= (help)
  33. ^ National Association for Public Safety GIS (NAPSG). "Use of the US National Grid to Enhance Situational Awareness & Define Operational Areas" (PDF). NAPSG. Retrieved 15 April 2019. {{cite web}}: Cite has empty unknown parameter: |dead-url= (help)
  34. ^ National Association for Public Safety GIS (NAPSG). "USNG and Pre-Scripted MIssions" (PDF). Retrieved 15 April 2019. {{cite web}}: Cite has empty unknown parameter: |dead-url= (help)
  35. ^ Delta State University (September 2017). "DSU Geospatial Information Technologies Center responds to Hurricane Harvey". Delta State University. Retrieved 4 March 2019. {{cite web}}: Cite has empty unknown parameter: |dead-url= (help)
  36. ^ Brooks, Talbot (2017). "Grid-Based Risk Modeling: A Standards Approach (OR: Saving the World One Grid Square at a Time)" (PDF). ESRI. Retrieved 16 April 2019 – via Proceedings of the 2017 ESRI National Security and Public Safety Summit. {{cite web}}: Cite has empty unknown parameter: |dead-url= (help)
  37. ^ Studt, Al (Lt.); Scott, Bruce (Capt.). "The USNG: It's Time to Stop Adopting and Start Implementing" (PDF). Florida Fire Service, October 2012. Retrieved 5 March 2019.
  38. ^ Studt, Al (Lt.) (November 2018). "Easy Geo-Location". The Volunteer Firefighter. Retrieved 10 March 2019.
  39. ^ ESRI. "Introducing the United States National Grid". Retrieved 2 March 2019. {{cite web}}: Cite has empty unknown parameter: |dead-url= (help)
  40. ^ Knippel, Randy (April 2018). "US National Grid: Get In The Game [video]". Vimeo. Retrieved 4 March 2019. {{cite web}}: Cite has empty unknown parameter: |dead-url= (help)
  41. ^ Florida Fire Chief's Association. "Position statement: US National Grid map updates and systems configuration". FFCA. Retrieved 2 March 2019. {{cite web}}: Cite has empty unknown parameter: |dead-url= (help)
  42. ^ Sperlongano, Jessica (29 April 2006). "Which Way to the National Grid?" (PDF). National Journal. Retrieved 2 March 2019.
  43. ^ West, Pat (20 July 2004). ""Get on the National Grid"" (PDF). Fire Chief Magazine. Retrieved 2 March 2019.
  44. ^ Charles, Dan (25 February 2006). ""New Kind of Map Could Help Emergency Response"". NPR.
  45. ^ USNGI. "USNG Institute". Retrieved 10 March 2019. {{cite web}}: Cite has empty unknown parameter: |dead-url= (help)

Further reading

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