show land surface
weather station
coverage.
Not even close to
being global coverage
before 1920, and still
not very good today.
Ocean coverage
is not shown --
it was even worse
than land coverage,
especially in the
Southern Hemisphere.
Weather satellite
temperature data,
available since 1979,
provide near-global
coverage, with small
areas around both poles
needing "infilling"
(guessing).
