• Welcome to the new nsidc.org! To get acquainted with what's changed, read our spotlight article: NSIDC.org website: New look and new features.

    Please note that we are in a beta launch of this website. During the beta phase, our website search may act unpredictably until the website stabilizes.

A Guide to EASE Grids

The Equal-Area Scalable Earth (EASE) Grids are intended to be versatile formats for global-scale gridded data, including remotely sensed data. Data can be expressed as a digital array with one of many possible grid resolutions, which are defined in relation to one of four possible projections: Northern / Southern Hemispheres (Lambert's equal-area, azimuthal), temperate zones (cylindrical, equal-area), or global (cylindrical, equal-area). 

Knowles (1993) states that "Two of the most important characteristics of maps are whether they are conformal or equal-area. No map projection is both, and some are neither." On conformal maps, angles within a small area are reproduced accurately so a small circle on the globe will look like a small circle on the map; by definition, the aspect ratio remains 1:1 everywhere, while the areal distortion varies, e.g. from -6% at the pole to +276% at the equator. On equal-area maps, a small circle placed anywhere on the map will always cover the same area on the globe, though the shape may be distorted. A very popular map that is neither conformal nor equal-area is the cylindrical equidistant map, also known as the lat-lon grid. This map suffers from both areal and shape distortion. The EASE Grids utilize an equal-area projection because that minimizes the amount of distortion over the poles, using the Northern and Southern Hemisphere projections, and on other key areas of the globe, using the temperate and global projections. Since areas don't change between grid cells, visualization and intercomparison operations are greatly simplified and analysis is more convenient.

There are currently two EASE Grids, referred to as EASE-Grid and EASE-Grid 2.0.

Comparison of EASE Grid Versions

     
    Feature EASE-Grid EASE-Grid 2.0
    Date Created 1992 2011
    Pole location Center of cell, polar grids cannot be nested Intersection of the four center cells, grids can be nested
    Nested Grids Cells can be nested if the grid extent is changed Coverage can stay the same, only the number of cells changes
    Corner Points Corner cell locations in azimuthal grids are undefined No undefined "off-the-Earth" corner cells 
    EPSG North: 3408
    South: 3409
    Global/Temperate: 3410
    North: 6931
    South: 6932
    Global/Temperate: 6933
    Datum International 1924 Authalic Sphere WGS 84
    GeoTIFF Requires reprojection1 Supported without reprojection
    Software Issues Usually requires user to understand custom projection settings1 Supported by most software
    1 Projection difficulties arise because the projection ellipsoid and reference datum are different, and most software assume they are the same

    References

    Knowles, Kenneth W. 1993. A Mapping and Gridding Primer: Points, Pixels, Grids, and Cells. Unpublished report to the National Snow and Ice Data Center, Boulder, Colorado USA.

    EASE-Grid: Brodzik, M. J. and K. W. Knowles. 2002. “Chapter 5: EASE-Grid: A Versatile Set of Equal-Area Projections and Grids.” in Michael F.Goodchild (Ed.) Discrete Global Grids: A Web Book. Santa Barbara, California USA: National Center for Geographic Information & Analysis. https://escholarship.org/uc/item/9492q6sm.

    EASE-Grid 2.0: Brodzik, M. J., B. Billingsley, T. Haran, B. Raup, M. H. Savoie. 2012. EASE-Grid 2.0: Incremental but Significant Improvements for Earth-Gridded Data Sets. ISPRS International Journal of Geo-Information, 1(1):32-45, doi:10.3390/ijgi1010032

    Brodzik, M. J., B. Billingsley, T. Haran, B. Raup, M. H. Savoie. 2014. Correction: Brodzik, M. J. et al. EASE-Grid 2.0: Incremental but Significant Improvements for Earth-Gridded Data Sets. ISPRS International Journal of Geo-Information 2012, 1, 32-45. ISPRS International Journal of Geo-Information, 3(3):1154-1156, doi:10.3390/ijgi3031154.


    Map projection details

    The four EASE Grid projections comprise two polar azimuthal equal-area projections for the Northern and Southern hemispheres, a global cylindrical equal-area projection, and a temperate zone cylindrical equal-area projection (figure below); the temperate projection is a subset of the global projection with different latitudinal bounds. More details about these four EASE Grid projections are available in Brodzik and Knowles 2002, Brodzik et al. 2012, and Brodzik et al. 2014. 

    EASE-Grid map projections: The Southern Hemisphere Azimuthal (top left), the Northern Hemisphere Azimuthal (top right), the Global Cylindrical (bottom), and the Temperate Cylindrical (bottom)

    EASE-Grid map projections: The Southern Hemisphere Azimuthal (top left), the Northern Hemisphere Azimuthal (top right), the Global Cylindrical (bottom), and the Temperate Cylindrical (bottom)

     

    Grid definitions

    Schematic showing the perfect nesting of the EASE-Grid 2.0 3 km, 9 km, and 36 km grids. — Credit: National Snow & Ice Data Center (NSIDC)

    Each EASE Grid projections can be covered by many different grids. These grids are, essentially, the parameters necessary to define a transparent piece of graph paper that is overlaid on a flat map and then anchored to it at the map origin. The following four elements completely describe a grid:

    • the map projection
    • the numbers of columns and rows
    • the area of each grid cell
    • the location of the map's origin

    Any number of grid definitions can therefore be used to describe the effect of changing the "graph paper." For example, doubling the number of columns or rows doubles the resolution; see Figure 2 for an example of how this scaling can produce a family of multi-resolution grids that nest within one another. Though the user has complete flexibility to define a custom grid for any EASE Grid projection, the tables below describe some common EASE Grids in detail. 

    1 km Resolution EASE Grids

    EASE Grid Version

    Projection

    Number of Columns

    Number of Rows

    Grid Cell Area

    x-axis map coordinate of the outer edge of the upper-left pixel

    y-axis map coordinate of the outer edge of the upper-left pixel

    EASE-Grid 2.0 Global, Equal-Area
    (EPSG: 6933)
    34,704 14,616 1000.90 m x 1000.90 m -17367530.45 7314540.83

    3 km Resolution EASE Grids

    EASE Grid Version

    Projection

    Number of Columns

    Number of Rows

    Grid Cell Area

    x-axis map coordinate of the outer edge of the upper-left pixel

    y-axis map coordinate of the outer edge of the upper-left pixel

    EASE-Grid 2.0 Global, Equal-Area
    (EPSG: 6933)
    11568 4872 3,002.69 m x 3,002.69 m -17367530.45 7314540.83
    EASE-Grid 2.0 Northern Hemisphere, Lambert Azimuthal
    ​(EPSG: 6931)
    6000 6000 3,000 m x 3,000 m -9000000.0 9000000.0
    EASE-Grid 2.0 Southern Hemisphere, Lambert Azimuthal
    ​(EPSG: 6932)
    6000 6000 3,000 m x 3,000 m -9000000.0 9000000.0

    3.125 km Resolution EASE Grids

    EASE Grid Version

    Projection

    Number of Columns

    Number of Rows

    Grid Cell Area

    x-axis map coordinate of the outer edge of the upper-left pixel

    y-axis map coordinate of the outer edge of the upper-left pixel

    EASE-Grid 2.0 Global, Equal-Area
    ​(EPSG: 6933)
    11104 4672 3,128.16 m x 3,128.16 m -17367530.45 7307375.92
    EASE-Grid 2.0 Northern Hemisphere, Lambert Azimuthal
    ​(EPSG: 6931)
    5760 5760 3,125 m x 3,125 m -9000000.0 9000000.0
    EASE-Grid 2.0 Southern Hemisphere, Lambert Azimuthal
    ​(EPSG: 6932)
    5760 5760 3,125 m x 3,125 m -9000000.0 9000000.0
    EASE-Grid 2.0 Temperate Zones, Cylindrical Equal-Area
    ​(EPSG: 6933)
    11104 4320 3,128.16 m x 3,128.16 m -17367530.45 6756820.20

    6.25 km Resolution EASE Grids

    Grid Name

    Projection

    Number of Columns

    Number of Rows

    Grid Cell Area

    x-axis map coordinate of the outer edge of the upper-left pixel

    y-axis map coordinate of the outer edge of the upper-left pixel

    EASE-Grid 2.0

    Global, Equal-Area
    ​(EPSG: 6933)

    5552

    2336

    6,256.32 m x 6,256.32 m

    -17367530.45

    7307375.92

    EASE-Grid 2.0

    Northern Hemisphere, Lambert Azimuthal
    ​(EPSG: 6931)

    2880

    2880

    6,250 m x 6,250 m

    -9000000.0

    9000000.0

    EASE-Grid 2.0

    Southern Hemisphere, Lambert Azimuthal
    ​(EPSG: 6932)

    2880

    2880

    6,250 m x 6,250 m

    -9000000.0

    9000000.0

    EASE-Grid 2.0

    Temperate Zones, Cylindrical Equal-Area
    ​(EPSG: 6933)

    5552

    2160

    6,256.32 m x 6,256.32 m

    -17367530.45

    6756820.20

    9 km Resolution EASE Grids

    Grid Name Projection Number of Columns Number of Rows Grid Cell Area x-axis map coordinate of the outer edge of the upper-left pixel y-axis map coordinate of the outer edge of the upper-left pixel
    EASE-Grid 2.0 Global, Equal-Area
    ​(EPSG: 6933)
    3856 1624 9,008.05 m x 9,008.05 m -17367530.45 7314540.83
    EASE-Grid 2.0 Northern Hemisphere, Lambert Azimuthal
    ​(EPSG: 6931)
    2000 2000 9,000 m x 9,000 m -9000000.0 9000000.0
    EASE-Grid 2.0 Southern Hemisphere, Lambert Azimuthal
    ​(EPSG: 6932)
    2000 2000 9,000 m x 9,000 m -9000000.0 9000000.0

    12.5 km Resolution EASE Grids

    Grid Name Projection Number of Columns Number of Rows Grid Cell Area x-axis map coordinate of the outer edge of the upper-left pixel y-axis map coordinate of the outer edge of the upper-left pixel
    EASE-Grid Global, Equal-Area
    ​(EPSG: 3410)
    2766 1171 12,533.76 m x 12,533.76 m -17327927.35 7338516.48
    EASE-Grid Northern Hemisphere, Lambert Azimuthal
    ​(EPSG: 3408)
    1441 1441 12,533.76 m x 12,533.76 m -9030574.08 9030574.08
    EASE-Grid Southern Hemisphere, Lambert Azimuthal
    ​(EPSG: 3409)
    1441 1441 12,533.76 m x 12,533.76 m -9030574.08 9030574.08
    EASE-Grid 2.0 Global, Equal-Area
    ​(EPSG: 6933)
    2776 1168 12,512.63 m x 12,512.63 m -17367530.45 7307375.92
    EASE-Grid 2.0 Northern Hemisphere, Lambert Azimuthal
    ​(EPSG: 6931)
    1440 1440 12,500 m x 12,500 m -9000000.0 9000000.0
    EASE-Grid 2.0 Southern Hemisphere, Lambert Azimuthal
    ​(EPSG: 6932)
    1440 1440 12,500 m x 12,500 m -9000000.0 9000000.0
    EASE-Grid 2.0 Temperate Zones, Cylindrical Equal-Area
    ​(EPSG: 6933)
    2776 1080 12,512.63 m x 12,512.63 m -17367530.45 6756820.20

    25 km Resolution EASE Grids

    Grid Name Projection Number of Columns Number of Rows Grid Cell Area x-axis map coordinate of the outer edge of the upper-left pixel y-axis map coordinate of the outer edge of the upper-left pixel
    EASE-Grid Global, Equal-Area
    ​(EPSG: 3410)
    1383 586 25,067.53 m x 25,067.53 m -17334193.54 7344784.83
    EASE-Grid Northern Hemisphere, Lambert Azimuthal
    ​(EPSG: 3408)
    721 721

    25,067.53 m x 25,067.53 m

    -9036842.76 9036842.76
    EASE-Grid Southern Hemisphere, Lambert Azimuthal
    ​(EPSG: 3409)
    721 721 25,067.53 m x 25,067.53 m -9036842.76 9036842.76
    EASE-Grid 2.0 Global, Equal-Area
    ​(EPSG: 6933)
    1388 584 25,025.26 m x 25,025.26 m -17367530.45 7307375.92
    EASE-Grid 2.0 Northern Hemisphere, Lambert Azimuthal
    ​(EPSG: 6931)
    720 720 25,000 m x 25,000 m -9000000.0 9000000.0
    EASE-Grid 2.0 Southern Hemisphere, Lambert Azimuthal
    ​(EPSG: 6932)
    720 720 25,000 m x 25,000 m -9000000.0 9000000.0
    EASE-Grid 2.0 Temperate Zones, Cylindrical Equal-Area
    ​(EPSG: 6933)
    1388 540 25,025.26 m x 25,025.26 m -17367530.45 6756820.20

    Table 8. 36 km Resolution EASE Grids

    Grid Name Projection Number of Columns Number of Rows Grid Cell Area x-axis map coordinate of the outer edge of the upper-left pixel y-axis map coordinate of the outer edge of the upper-left pixel
    EASE-Grid 2.0 Global, Equal-Area
    ​(EPSG: 6933)
    964 406 36,032.22 m x 36,032.22 m -17367530.45 7314540.83
    EASE-Grid 2.0 Northern Hemisphere, Lambert Azimuthal
    ​(EPSG: 6931)
    500 500 36,000 m x 36,000 m -9000000.0 9000000.0
    EASE-Grid 2.0 Southern Hemisphere, Lambert Azimuthal
    ​(EPSG: 6932)
    500 500 36,000 m x 36,000 m -9000000.0 9000000.0

    Other useful articles

    NSIDC EASE Grid Data sets

    Many NSIDC data products use EASE Grids. Explore NSIDC Data

    Section