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The Natural Resources Canada topographic map A 741, 83 C/7, edition 3 has a (bilingual) indication at the bottom stating:

WEST OF FIFTH MERIDIAN       OUEST DU CINQIÈME MÉRIDIEN

What does this mean? It's around 117°W, so it is indeed west of the 5th meridian, but I think something else is meant here. Does this have a specific meaning on a topographic map?

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As Michael alludes to in a comment, this notation is related to the Dominion Land Survey (Canada) in your case, or the Public Land Survey System (United States) in mine, which the DLS is based on. Those systems are nested series of grids whose top level of reference are principal meridians and baselines. Because of the way the system is set up and numbered, grid cells ultimately must reference being east or west of a principal meridian. For example Section 3, Township 5 North, Range 68 West of the Sixth Principal Meridian. Similar to UTM where if you just give a number you could be referring to either north or south.

Related question: Does anyone use TRS (Township, Range, Section) data?

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The prime meridian passes through Greenwich, but how many meridians are there to be the 5th of? In reality the could be a great many but I think they are referring to the Fifth Principal Meridian

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  • Aha. But why do they write that on this particular map? It seems arbitrary. – gerrit Apr 24 '14 at 2:12
  • It means nothing to me here in Australia but must be important to somebody. The Wiki article states governs the surveys in all or most of six states so that might be worth noting. – Michael Stimson Apr 24 '14 at 2:19

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