Hi. I've done a little searching around and haven't been able to find an answer/solution to the question: How can I view the declination for my current location? Old school offline [read, paper] maps usually include a declination for determining True North (versus magnetic north). Does OSM include this information and, if so, how can I view it for my current location?

Scenario: I'm out hiking, no cell service, GPS is spotty (or is broken), and I'm relying on downloaded offline maps.

Thanks in advance!

asked 06 Sep, 18:35

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lost_signal
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edited 06 Sep, 20:39


Depends on your downloaded, offline maps. I am not aware of a way to see declination on OsmAnd nor do I use Gaia or other hiking specific apps. I do use Avenza Maps which uses geo-referenced PDFs and those PDFs often have both the map date and the declination at the time the PDF was create on the margin. (Disclosure: I create my own hiking maps from OSM data. My maps are modeled after the older USGS topographic maps so have the same type of declination information on them as the old paper maps.)

The work around I would use in your case would be to go to the NOAA declination lookup site before trip(s) and get the value for the center of your hike.

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answered 06 Sep, 20:58

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n76
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Thanks. Yeah, I've used the NOAA declination lookup and know my declination for the city where I live. I was just wondering if OSM (and OSMAnd) had the capacity to basically calculate declination based on $currentlocation, if I'm out hiking or whatever.

I'm curious how your modelling your maps off older USGS maps benefits you, given that old paper maps need to be updated every few years based on a shifting magnetic north.

(06 Sep, 21:18) lost_signal

"Modeling" meaning the style sheets my scripts use attempt to mimic that older USGS style.

To create a map of an area, I give my scripts the lower right lat/lon for the map I want, name of map, coverage size, scale, etc. The scripts, among other things, grab the NOAA declination for the map center based on current NOAA model/data. Trails, roads, streams, buildings, etc. are from OSM while data for contours, etc. is from the USGS. Final result is a geo-reference PDF complete with margin information showing declination that I can either print (with a big enough printer) and/or load into Avenza Maps for use in the field.

With respect to update interval, I run the scripts when I feel like I need an updated map of the area I will be going to. I also sell some of my maps on the Avenza Map store, update interval for that is a couple of times a year. More often if I notice significant updates in an area in the OSM data.

See: https://tods-topos.fitchfamily.org for more information.

(06 Sep, 22:00) n76

I just checked Locus Map and it shows declination on its compass. I have no idea, though, where it takes the data from. OpenStreetMap data do not hold such information.

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answered 07 Sep, 08:47

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TZorn
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As said in your other question, OsmAnd can display bearings, true and magnetic, so it knows about the declination.

Maybe you can ask for a dedicated declination widget, in their repository there's already a related issue.

Regards.

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answered 07 Sep, 11:20

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H_mlet
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I would think difference between mag and true IS the declination. Couldn't you just write that on your emergency paper map before you set off. If you need to check locally, you could try a goto lat long 0,0 on a gps should show true north. and a goto lat 86.50 long 164.04 will show that bearing and the difference is the declination. Or have I got this all wrong?

(07 Sep, 14:49) andy mackey
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question asked: 06 Sep, 18:35

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last updated: 07 Sep, 14:51

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