
NDFD Spatial Reference System
NDFD Grids
NDFD data are stored as points on regular grids. There are 6 grids with each grid derived
from points projected from a sphere of radius 6371.2 km. The CONUS and Northern Hemisphere
grids use a Lambert Conformal projection while the Guam, Hawaii, Puerto Rico, and Northern Pacific
grids use a Mercator projection. The Alaska grid is based on a Polar Stereographic projection.
Additional metadata on NDFD grids are available in
three grid definition tables below.
NDFD Horizontal Datum
NDFD Vertical Datum
Grid Locations and Extent
The NDFD grids, as described in the tables below, are the result of projecting a sphere onto a
flat surface. The corner of the grid is found at the point identified in the grid parameters tables
as latitude1 and longitude1. Each table lists the number of points in the grid which is the product of
the number of points on the parallel and meridian. Grid points are seperated by Dx meters along the x
axis (longitude) and Dy meters along the y axis (latitude). The projection type, earth radius, and
other grid definition parameters are provided in the tables below. For more
information on decoding GRIB2 files, see the section on GRIB2 Links.
CONUS and Northern Hemisphere Grids
Grid Parameter 
CONUS 5km 
CONUS 2.5km 
Northern Hemisphere 
Number of Points 
739297 
2953665 
1509825 
Projection Type 
Lambert Conformal 
Lambert Conformal 
Lambert Conformal 
Shape of Earth 
sphere 
sphere 
sphere 
Earth Radius 
6371.2 km 
6371.2 km 
6371.2 km 
Number of Points on the parallel 
1073 
2145 
1473 
Number of Points on the Meridian 
689 
1377 
1025 
Latitude1 
20.191999 
20.191999 
12.189999 
Longitude1 
238.445999 
238.445999 
226.541000 
u/v vectors relative to 
easterly/northerly 
easterly/northerly 
easterly/northerly 
Dx 
5079.406 m 
2539.703 m 
5079.406 m 
Dy 
5079.406 m 
2539.703 m 
5079.406 m 
GRIB2 grid, scan mode 
64 (0100) 
64 (0100) 
64 (0100) 
Scan i/x direction 
positive 
positive 
positive 
Scan j/y direction 
positive 
positive 
positive 
Consecutive points in 
i/x direction 
i/x direction 
i/x direction 
Adjacent rows scan in 
same direction 
same direction 
same direction 
Mesh Latitude 
25 
25 
25 
Orientation Longitude 
265 
265 
265 
Which Pole is on the Plane 
north 
north 
north 
Is Projection Bipolar 
no 
no 
no 
Tangent Latitude1 
25 
25 
25 
Tangent Latitude2 
25 
25 
25 
Southern Latitude 
90 
90 
90 
Southern Longitude 
0 
0 
0 
Guam, Hawaii, Puerto Rico Grids, Northern Pacific and Oceanic Grids
Grid Parameter 
Guam 
Hawaii 
Puerto Rico 
N. Pacific 
Oceanic 
Number of Points 
37249 
72225 
75936 
1580529 
4512981 
Projection Type 
Mercator 
Mercator 
Mercator 
Mercator 
Mercator 
Shape of Earth 
sphere 
sphere 
sphere 
sphere 
sphere 
Earth Radius 
6371.2 km 
6371.2 km 
6371.2 km 
6371.2 km 
6371.2 km 
Number of Points on the parallel 
193 
321 
339 
1473 
2517 
Number of Points on the Meridian 
193 
225 
224 
1073 
1793 
Latitude1 
12.349884 
18.072699 
16.977485 
25.000000 
30.4192 
Longitude1 
143.686538 
198.474999 
291.972167 
110.000000 
129.906000 
u/v vectors relative to 
easterly/northerly 
easterly/northerly 
easterly/northerly 
easterly/northerly 
easterly/northerly 
Latitude2 
16.794399 
23.087799 
19.544499 
60.643999 
79.991525 
Longitude2 
148.280000 
206.130999 
296.015600 
250.871000 
10.689223 
Dx 
2500.0 m 
2500.0 m 
1250.0 m 
10000.0 m 
10000.0 m 
Dy 
2500.0 m 
2500.0 m 
1250.0 m 
10000.0 m 
10000.0 m 
GRIB2 grid, scan mode 
64 (0100) 
64 (0100) 
64 (0100) 
64 (0100) 
64 (0100) 
Scan i/x direction 
positive 
positive 
positive 
positive 
positive 
Scan j/y direction 
positive 
positive 
positive 
positive 
positive 
Consecutive points in 
i/x direction 
i/x direction 
i/x direction 
i/x direction 
i/x direction 
Adjacent rows scan in 
same direction 
same direction 
same direction 
same direction 
same direction 
Mesh Latitude 
20 
20 
20 
20 
20 
Orientation Longitude 
0 
0 
0 
0 
0 
Tangent Latitude1 
0 
0 
0 
0 
0 
Tangent Latitude2 
0 
0 
0 
0 
0 
Southern Latitude 
0 
0 
0 
0 
0 
Southern Longitude 
0 
0 
0 
0 
0 
Alaska Grid
Grid Parameter 
Alaska 
Number of Points 
456225 
Projection Type 
Polar Stereographic 
Shape of Earth 
sphere 
Earth Radius 
6371.2 km 
Number of Points on the parallel 
825 
Number of Points on the Meridian 
553 
Latitude1 
40.530101 
Longitude1 
181.429000 
u/v vectors relative to 
easterly/northerly 
Dx 
5953.125 m 
Dy 
5953.125 m 
GRIB2 grid, scan mode 
64 (0100) 
Scan i/x direction 
positive 
Scan j/y direction 
positive 
Consecutive points in 
i/x direction 
Adjacent rows scan in 
same direction 
Mesh Latitude 
60 
Orientation Longitude 
210 
Which Pole is on the Plane 
north 
Is Projection Bipolar 
no 
Tangent Latitude1 
90 
Tangent Latitude2 
90 
Southern Latitude 
0 
Southern Longitude 
0 
For users interested in processing GRIB2 files, there is a wealth of online resources to
assist you will understanding the specification and decoding file contents. The following links
will help you tap into this treasure trove of information:
