We divide Greenland, including its peripheral glaciers and ice caps, into 260 basins grouped in seven regions:  southwest (SW), central west (CW), (iii) northwest (NW), north (NO), northeast (NE), central east (CE), and southeast (SE). These regions are selected based on ice flow regimes, climate, and the need to partition the ice sheet into zones comparable in size (200,000 km2 to 400,000 km2) and ice production (50 Gt/y to 100 Gt/y, or billion tons per year). Out of the 260 surveyed glaciers, 217 are marine-terminating, i.e., calving into icebergs and melting in contact with ocean waters, and 43 are land-terminating.The actual number of land-terminating glaciers is far larger than 43, but we lump them into larger units for simplification.

Each glacier catchment is defined using a combination of ice flow direction and surface slope. In areas of fast flow (> 100 m), we use a composite velocity mosaic (Mouginot et al. 2017). In slowmoving areas, we use surface slope using the GIMP DEM (https://nsidc.org/data/nsidc- 0715/versions/1) (Howat et al. 2014) smoothed over 10 ice thicknesses to remove shortwavelength undulations.

References:

Mouginot J, Rignot E, Scheuchl B, Millan R (2017) Comprehensive annual ice sheet velocity mapping using landsat-8, sentinel-1, and radarsat-2 data. Remote Sensing 9(4).

Howat IM, Negrete A, Smith BE (2014) The greenland ice mapping project (gimp) land classification and surface elevation data sets. The Cryosphere 8(4):1509–1518.