Locations of the weather (surface pressure) observations being used to reconstruct global weather and climate.
Observations coverage (1851-2008) in version 3.2.9 of the International Surface Pressure Databank (that used in the Twentieth Century Reanalysis version 2c). Each frame shows all the observations for a 3-day period.
This dataset contains 1,399,120,833 observations over this period. Many more historical observations exist (on paper, or in restricted access collections). These are the ones that are currently available to science.
Rendered at NERSC (nersc.gov).