The Landsat GeoCover 2000 collection of global imagery was subset by the GLCF
into 20 kilometer squares centered on every intersection of one degree latitude and one degree
longitude. This collection is intended as a sample of the complete Landsat coverage
for use in global modeling. The original Landsat imagery is too large for storage
and processing in most global modeling operations, so subsets are made available.
Also, note there is an unaffiliated group documenting degree intersections,
providing often valuable, but personal, photographs of ground conditions: The Degree Confluence Project.