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The two grids are based on different map projections. The polar stereographic projection was initially used with ice concentration products developed at the NASA Goddard Space Flight Center (GSFC) and has been retained for historical consistency. It specifies a projection plane tangent to the earth at 70° latitude, which was selected so that little or no distortion would occur in the marginal ice zone. For a more in-depth description, see the Polar Stereographic Projection and Grid Web page at https://nsidc.org/support/faq/guide-nsidcs-polar-stereographic-projection.
The Equal-Area Scalable Earth (EASE) Grids are based on a philosophy of digital mapping and gridding definitions developed at NSIDC. It is intended to be a versatile tool for users of global-scale gridded data, specifically remotely sensed data, although it is gaining popularity as a common gridding scheme for data from other sources as well. Both EASE-Grid and EASE-Grid 2.0 consists of a set of three equal-area projections, combined with an infinite number of possible grid definitions. It allows diverse data sets to be compared on the same grid. For a more in-depth description, see the EASE Grids web page at https://nsidc.org/support/faq/guide-ease-grids.