PDF printed Declination change

James Mellinger's Avatar

James Mellinger

28 Aug, 2020 11:24 PM

does the declination reflect the current date saved or in usgs topos date surveyed? the caltopo doesn't print the date of the declination nor does it print amount of change per year.

  1. 1 Posted by James Mellinger on 29 Aug, 2020 12:30 AM

    James Mellinger's Avatar

    I live in northern western usa the north west declination is somewhere around 14 or more degrees. for example etna california had the following declination info.in 2004 15 degrees plus .7 degrees Positive west declination its 2020 2004- 2020= 16
    16 x .7 degrees equal 11.2..your end result is 26.2 degree west declination..my suggestion head for the hills get out of the woods and triangulate prominent mountains. please fix me..how can it move this much..I'm no math genius..but seems serious to me.
    I've heard two differnt treads, yes take declination seriously and NOT take it serious if lass than 10 miles/15k..WTFO.

  2. Support Staff 2 Posted by Julie on 31 Aug, 2020 03:21 PM

    Julie's Avatar

    Hi James,

    The declination is calculated at the time the PDF is produced and should be up-to-date with the magnetic field at that time.

    Best,
    Julie

  3. Julie closed this discussion on 31 Aug, 2020 03:21 PM.

  4. Ben Lantow re-opened this discussion on 01 Sep, 2020 09:06 PM

  5. Support Staff 3 Posted by Ben Lantow on 01 Sep, 2020 09:06 PM

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    Hi there, I just want you to know I went and double checked all the declination data. The data set did change in 2020 for the next 5 years, and we are going to update to the 2020-2025 model from the 2015-2020 model but this is the overlap year.

    The current declination in that area is 14 degrees (at the summit of Mount Shasta) based on both the 2015-2020 model and the 2020-2025 models. See links here:

    https://caltopo.com/p/146B
    https://www.magnetic-declination.com/USA/Mount%20Shasta/2733243.html

    Declination is going to vary widely based on N-S position as well as E-W position, and every 5 years the magnetic model is updated to reflect the shifting magnetic fields and poles. Trying to figure out something for 2004 is not going to be accurate and is very dated since the models change regularly.

    Our maps don't print a rate of change because as Julie referenced they are accurate for the time they are printed. If you need a new map several years later the best thing to do is recreate and recalculate it.

    That said 1 degree of error over 10miles is extremely small and you will be right in the ballpark of where you're headed.

    Best,
    Ben

  6. Ben Lantow closed this discussion on 01 Sep, 2020 09:06 PM.

  7. James Mellinger re-opened this discussion on 02 Sep, 2020 03:22 AM

  8. 4 Posted by James Mellinger on 02 Sep, 2020 03:22 AM

    James Mellinger's Avatar

    Thank you that has cleared the mud up a bit..to clarify every map I
    print will be the same declination till next model is updated ..correct?

  9. 5 Posted by fogmachine on 02 Sep, 2020 04:07 AM

    fogmachine's Avatar

    There was a February 2019 release of the World Magnetic Model that was out-of-cycle, meaning it was rushed ahead of schedule because the poles are drifting faster than expected. The 2020 release was in December 2019 and should be good until 2025 since drift should slow but it's something to keep an eye on.

    The poles move around quite a bit more than many think.
    https://en.wikipedia.org/wiki/Polar_drift

  10. Support Staff 6 Posted by Julie on 02 Sep, 2020 02:33 PM

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    James,

    Yes, each map you print for the same location will have the same declination at that location until the next model updates.

  11. Julie closed this discussion on 02 Sep, 2020 02:33 PM.

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