PM has various meanings in the Geography category. Discover the full forms, definitions, and usage contexts of PM in Geography.
That meridian from which longitude is reckoned By common consent this is now the meridian of Greenwich Originally, was that meridian on which the magnetic variation of compass was zero in a certain latitude Has varied in longitude between Jerusalem and Brazil, but most frequently through Azores and Canary Islands First passed through London (St Paul's Cathedral) in 17th century First drawn through Greenwich, 1794.
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