The USNG is an alpha-numeric reference system that overlays the UTM coordinate system. A USNG spatial address is broken down into three parts, the; - Grid Zone Designation; for a world-wide unique address. - 100,000-meter Square Identification; for regional areas. - Grid Coordinates; for local areas.
4 digits - 2306 - locates a point with a precision of 1,000-meters (a neighborhood size area). 6 digits - 234064 - locates a point with a precision of 100-meters (a soccer field size area). 8 digits - 23480647 - locates a point with a precision of 10-meters (the size of a modest home). 10 digits - 2348306479 - locates a point with a precision of 1-meter (within a parking spot).
To review, we can see a complete US National Grid spatial address contains three parts as we drill down to a unique location, 18S UJ 23480647 - Grid Zone Designation (i.e. 18S). - 100,000-meter Square Identification (i.e. UJ ). - Grid coordinates of some even number of digits ranging from 2 to 10 (i.e. 23480647 In this case, eight digits identify a place of about the size of a modest home.). You always read right, then up when plotting coordinates.
A spatial address is customarily written as a single string of values. Note how the horizontal datum (NAD 83) has been included: USNG: 18SUJ23480647 (NAD 83)
Floridadisaster.org --------------------------------------------------------------- In an effort to standardize maps in Florida for both emergency and other operations, the State Fire Marshal, as the coordinating agency for search and rescue under the State Comprehensive Emergency Management Plan, and the Division of Emergency Management are embarking on a program to adopt the US National Grid (USNG) as the standard in Florida. This project will ensure a uniform grid mapping system across cities and counties in Florida, and will match the system used by the National Guard, the US Coast Guard and the US military when they are deployed into our state.
Floridas unique geography of miles of coastlines, multiple river corridors, and large watersheds make the use of the common Township/Range/Section grid (PLSS) all but impossible except for a handful of inland counties. As the grid approaches wetlands, river corridors and the coast line, sections become irregular in shape and can be significantly larger than the typical square mile, which is too large to accommodate the needs of ground crews.
Adoption of a national grid system has been identified as critical in a number of after action reports, investigations and studies dating as far back as Hurricane Andrew. FEMA, DHS, the National GeoSpatial Intelligence Agency, and the Federal Geographic Data Committee all promote the adoption of the USNG.
Grid cell values are unique and sequentially numbered.
A note about data scale:
Scale is an important factor in data usage. Certain scale datasets are not suitable for some project, analysis, or modeling purposes. Please be sure you are using the best available data.
1:24000 scale datasets are recommended for projects that are at the county level. 1:24000 data should NOT be used for high accuracy base mapping such as property parcel boundaries. 1:100000 scale datasets are recommended for projects that are at the multi-county or regional level. 1:125000 scale datasets are recommended for projects that are at the regional or state level or larger.
Vector datasets with no defined scale or accuracy should be considered suspect. Make sure you are familiar with your data before using it for projects or analysis. Every effort has been made to supply the user with data documentation. For additional information, see the References section and the Data Source Contact section of this documentation. For more information regarding scale and accuracy, see our webpage at: <http://geoplan.ufl.edu/education.html>
Guidelines for Building US National Grid Polygons with ArcGIS <http://floridadisaster.org/gis/usng/Documents/build_usng_polygons.pdf>
Next the XTools Add XY function was used to produce X and Y coordinates for each polygon.
Added fields: X_LWRLFT, Y_LWRLFT, GRID100K, GRID10K, GRID1000M, LABEL, DESCRIPT, FGDLAQDATE, and AUTOID.
Calculated the AUTOID field as follows; [FID] + 1
Created Centroids for the 1000M Grid and spatially joined it to the existing usng_fl_10k_utm17.shp Grid.
Joined the Centroids with the 10K Grid information back to the 1000M Grid, via a table join based on AUTOID.
Calculated the GRID100K field based on the joined GRID100K field from the Centroids.
Calculated the GRID10K field based on the joined GRID10K field from the Centroids.
Calculate X_LWRLFT and Y_LWRLFT values as follows; Round ( [XCOORD] - 500, 0 ) Round ( [YCOORD] - 500, 0 ) After these calculations, the XCOORD and YCOORD fields may be deleted.
Calculate GRID1000M as follows; Mid ( [X_LWRLFT] , 2, 2 ) + " " + Mid ( [Y_LWRLFT] , 3 ,2 )
Calculate LABEL as follows; [GRID100K] + " " + Mid ( [X_LWRLFT] , 2, 2 ) + Mid ( [Y_LWRLFT] , 3 ,2 )
Calculated DESCRIPT based on LABEL.
After field calculations were completed the join was removed.
For more information on field calculations please see Guidelines for Building US National Grid Polygons with ArcGIS <http://floridadisaster.org/gis/usng/Documents/build_usng_polygons.pdf>
Next the XTools Add XY function was used to produce X and Y coordinates for each polygon.
Added fields: X_LWRLFT, Y_LWRLFT, GRID100K, GRID10K, GRID1000M, LABEL, DESCRIPT, FGDLAQDATE, and AUTOID.
Calculated the AUTOID field as follows; [FID] + 250,001
Created Centroids for the 1000M Grid and spatially joined it to the existing usng_fl_10k_utm16.shp Grid.
Joined the Centroids with the 10K Grid information back to the 1000M Grid, via a table join based on AUTOID.
Calculated the GRID100K field based on the joined GRID100K field from the Centroids.
Calculated the GRID10K field based on the joined GRID10K field from the Centroids.
Calculate X_LWRLFT and Y_LWRLFT values as follows; Round ( [XCOORD] - 500, 0 ) Round ( [YCOORD] - 500, 0 ) After these calculations, the XCOORD and YCOORD fields may be deleted.
Calculate GRID1000M as follows; Mid ( [X_LWRLFT] , 2, 2 ) + " " + Mid ( [Y_LWRLFT] , 3 ,2 )
Calculate LABEL as follows; [GRID100K] + " " + Mid ( [X_LWRLFT] , 2, 2 ) + Mid ( [Y_LWRLFT] , 3 ,2 )
Calculated DESCRIPT based on LABEL.
After field calculations were completed the join was removed.
For more information on field calculations please see Guidelines for Building US National Grid Polygons with ArcGIS <http://floridadisaster.org/gis/usng/Documents/build_usng_polygons.pdf>
Next the UTM Zone 17N and UTM Zone 16N shapefiles were reprojected to the FGDL Albers projection (NAD83 Albers HPGH).
Next selections were taken from each UTM zone where as they did not interest each other. These two selections were then appended together to create a statewide layer where areas containing the over lap contained no data.
Next each zone was selected for where features overlaped each zone and these overlap features were exported for each shapefile.
Each exported zones over lap features were then erased, this erase was base on features falling outside their designated 100K grid, this erase was based on the usgn_fl_100k.shp
Next the remaining parts of the two erased zone shapefiles were appended back to the statewide 1K layer creating a continuous statewide 1K layer.