Compasses

[bzachar]

Hi Kids,

This came up in another hiking forum I participate in and I wanted to pass it along. Enjoy!

Bill


[ dead link removed ]

[Nighthiker]

I find more Brunton than anything else left along the trail, almost all Silva's were the forestry model. Though I night hike quite a bit, I do not have a compass with a luminous dial.

[plummer150]

Looks like that website could be helpful and interesting. However, that too much to read for me. Maybe next time.

[hegstrom]

I haven't spent a lot of time thinking about or using a compass. We're day hikers, so it's not like we go off hiking uncharted territory.

However, most often, I will purchase take along the quad map(s) of the area we're hiking and I do have one of those tiny little thermometer/compass things that hangs off the zipper of my day pack. So far, I've only used the thermometer.

Of the places that we day hike I'd find it very tough to get lost. Usually it is fairly open country or your in a canyon with a creek to follow.

We just got back from backpacking the GC from North Rim to South Rim. There the trails are so wide and obvious you'd really have a hard time getting lost.

[mttgilbert]

even if you don't ever need a compass, its still a good idea to have one and know how to use it. I've always carried a compass but I've only needed it once. And I'll tell ya' I don't know what I would have done if I hadn't had the compass. Sometimes unexpected things happen, I think its best to be prepared whatever the odds.

[Nighthiker]

I have noted a couple of times folks who use a compass do not recheck or adjust declination when using a compass in the valley area and then hiking in Rim country. I was taught when moving 100 miles check your declination. Though I have a lot of USGS topo maps that I utilize, I use the current declination and not what is labeled on the maps.

[Grasshopper]

Though I have a lot of USGS topo maps that I utilize, I use the current declination and not what is labeled on the maps.

I don't understand . What is the current declination you mention? and are you saying that you are finding that the official declination noted on the Topo Maps is sometimes not correct?

[chumley]

Compass? You mean the Jeep?

[big_load]

Though I have a lot of USGS topo maps that I utilize, I use the current declination and not what is labeled on the maps.

I don't understand . What is the current declination you mention? and are you saying that you are finding that the official declination noted on the Topo Maps is sometimes not correct?

Most maps include an annual rate of change. It's pretty slow, though, especially compared to scale resolution and manual pointing error.

[Nighthiker]

My map collection goes back to the early 1920's and different editions of the same map may have different declinations labeled on them. I may be using a map from the 1930's for the Sierra Ancha area and the actual magnetic declination may be different then labeled on the map.

For those of you who use GPS with an actual map, take note of the map datum. It may list 1927 NAD but you GPS may be set to 1984 NAD.

[amy1300]

@Grasshopper
I just finished reading a small book "Wilderness Navigation" (by Bob Burns and Mike Burns) that explains why declination changes over time. They say it's because the earth's core (and therefore a lot of the metal elements that are part of why there's a magnetic field) is molten and sloshing around as the earth spins. It sloshes slowly, though . . .

You can get the current declination for a location by putting its latitude and longitude into the blanks at this site: https://www.ngdc.noaa.gov/geomag-web/#declination
I just did this with my Flagstaff Trails map (the margin of which says to use 13.5 degrees East as the declination for the area). The latitude and longitude figures are also in the margins of the map, and the site at the above link tells me that currently the declination for the same area covered by the map is 10.33 degrees East today - so the declination is off by more than 3 degrees from what the map states in its margin. It's changing by about 1 degree per 10 years, in Arizona, according to "Wilderness Navigation." So I'm guessing my map, even though it's dated "Seventh Edition February 2016" is based on some old data. (It gives 1927 and 1929 as two different kinds of "datum" to know, for GPS users - which I'm not.)

[Grasshopper]

You can get the current declination for a location by putting its latitude and longitude into the blanks at this site: ngdc.noaa.gov/geoma ... tion

Your discussion and this NOAA- Magnetic Declination Estimated Value link you note is interesting. Plugging in my residence zip code, I have learned that my GPS coordinate changes by 0° 6' W per year.. I had no idea!

Now I'm wondering how the current declination for any location in my Garmin GPS (with the old 1:24k topo maps I have loaded for AZ,NM.UT,CO) are dealt with when using my GPS to navigate from one location to another? I do recall when initially setting up navigation parameters in a GPS, that we have the option to set declination to either magnetic north or true north. I always set my GPS navigation to "true north" and fortunately so far I have always come back but now learning of this ongoing through the years, location coordinates magnetic declination changing, I now question how accurate our GPS navigating is, now using mostly available older (many years older) topo maps?

The 3 degrees map declination "delta" you site in your reply narrative could be a big problem if you are lost (and not knowing about the 3 degree delta to add or subtract for your compass declination) and only have that map to use for your map and compass navigation to go from Point A (where you are lost) to Point B (where you hope to not be lost).

[azbackpackr]

Wow! I had no idea! Thanks for the post.

[amy1300]

The 3 degrees map declination "delta" you site in your reply narrative could be a big problem if you are lost (and not knowing about the 3 degree delta to add or subtract for your compass declination) and only have that map to use for your map and compass navigation to go from Point A (where you are lost) to Point B (where you hope to not be lost).

Yeah, once I'd learned this I was kinda surprised the declination was printed on my map, without the year or any caution about it changing over time. You can bet I wrote in the current declination and the year, in the margin!

[Nighthiker]

Thanks for posting the NGDC link, very informative.

[HAZardous]

Now I'm wondering how the current declination for any location in my Garmin GPS (with the old 1:24k topo maps I have loaded for AZ,NM.UT,CO) are dealt with when using my GPS to navigate from one location to another?

It's not much of a problem. Your GPS is pointing you to a location, not in a direction. If your GPS has an electronic compass in it, and the declination table is slightly off, you will start off in slightly the wrong direction. But as you walk, the pointer will keep correcting as you get nearer your destination. In essence, you will walk in a slight arc. In reality, you will likely be navigating around bigger obstacles like ridges, streams, and thickets that require excursions that dwarf the arc error. If your GPS does not have a compass, or the compass is shut off, or if you are moving fast enough, your GPS uses the change in your position over time to determine your direction of travel, and the earth's magnetic field isn't used at all.

[Nighthiker]

I prefer and enjoy using a map and compass for land navigation. The picture depicts so very good reference materials and tools for plotting a course on a paper map. I utilize a USGS 7.5 minute map plot a course and make a copy in case I am over due. I prefer a map over a GPS because I can review a map and determine where I want to go while a GPS will tell me where to go.

The compasses depicted in the picture are: Top Left, a Silva Boy Scout model awarded to me the night I was promoted to Second Class Scout. Middle Left, Silva base plate Compass. Bottom Left a Brunton True Arc 10 Compass with a Global Needle that also features 1 degree bearings and Roamer scales. Top right Silva Ranger model with a flip up mirror and sight, usefull if you are new to triangulating your position. Far right Azimuth Compass Protractor. Bottom map ruler.

[azbackpackr]

I prefer maps as well. With a map you get a much better feel for where you are on the landscape.

Nice compass collection.

[CannondaleKid]

I prefer a map over a GPS because I can review a map and determine where I want to go while a GPS will tell me where to go.

I agree maps do offer many benefits over a GPS, but there are benefits of the GPS over a map as well... it's up to which is best for the individual.

In my case, a GPS is the best option, among the reasons being I can also review a GPS (map) and determine where I WANT to go.
And like your map, my GPS doesn't talk so it isn't able to tell me where to go.

Also, since most of my route planning is done ahead of time (including uploading a tentative route to my GPS) yes, there will be times when I stop, look at the terrain and wonder, 'what's over that rise' then consult the MAP on my GPS in the same manner you consult your map, and decide which way I wish to go... except I wouldn't have to dig out a map and unfold it on a windy/rainy day. Plus I can quickly zoom in or out as I wish.

[The_Eagle]

@CannondaleKid
For all those reasons, plus being able to navigate at night when you can't see land features. I grew up on maps/compass and over the years have shed carrying maps.
I am still a map person and love scanning maps both paper and electronically.