GLOBE Land Units (GLUs)
To enable real-time global analysis, GLOBE stratifies Earth’s land surface into GLOBE Land Units (GLU), a set of 1.445 million equal-area hexagons based on the geodesic Discrete Global Grid (DGG) system of Kevin Sahr (Sahr 2001; Sahr et al. 2003). Specifically, GLOBE is based on an ISEA3H Level 12 DGG, generated using DGGRID software version 3.1.
Each GLU (hexagonal cell) covers an area of approximately 100 km² (96 km²), and has an inter-cell spacing of 10.5 km.
Each GLU has a unique integer ID code (GLU_ID).
The complete set of GLUs are a subset of the full geodesic DGG covering all of Earth’s land, and were selected based on the spatial extent (land mask) of the LandScan 2007 global population density dataset (Dobson et al. 2000; 30 arc second resolution). All GLUs that contained at least one LandScan pixel (including 0 population) were selected for use in GLOBE. Land area within each GLU was calculated based on land coverage in LandScan 2007.
Global Variable values are calculated within each cell, including it’s land area (GLOBE calculations are based on land area within each GLU).
An example of GLUs covering Washington, D.C., USA and Baltimore, Maryland, USA is seen below.
- ESRI Shapefile (polygons; GLU unique ID = “GLU_ID”): <globe_glu_shapefile.zip>
- ESRI GRID (binary) (30 arc second raster; GLU unique ID = “VALUE” and = “GLU_ID”): <globe_grid_30s.zip>
Dobson, J. E., E. A. Bright, P. R. Coleman, R. C. Durfee, and B. A. Worley. 2000. LandScan: a global population database for estimating populations at risk. Photogrammetric Engineering and Remote Sensing 66:849-857. [download pdf]
Sahr, K. 2001. User Documentation for Discrete Global Grid Generation Software (DGGRID version 3.1b). [link]
Sahr, K., D. White, and A. J. Kimerling. 2003. Geodesic discrete global grid systems. Cartography and Geographic Information Science 30:121(114). [download pdf]
Current site: http://discreteglobalgrids.org/