For brevity (and because it's late and I need to get to bed) I will lump replies to a couple of comments together.

To KenK regarding datums: To be strictly correct, newer USGS topos use NAD83. However, functionally, NAD83 = WGS84. My understanding is that the difference between WGS84 and NAD83 is less than 1 meter (usuually much less than 1 meter). Even the potential difference between NAD27 and WGS84/NAD83 is not huge in most cases. In my area (Southcentral Alaska) it amounts to ~115 meters. Some areas may be more than that, but usually little more than a couple of hundred meters. Back in the dark ages before GPS, we were often thrilled to fix our position to within 200 meters.

To hikermore regarding magnetic declination diagrams:This is correct, assuming one is orienting the map to terrain (which is what one does ~99% of the time). However, the comment was in reference to using the compass to orient the map. The implication (at least to me) of the comment I referenced was that someone could just align magnetic north from the compass parallell with the magnetic north line on the little diagram, to orient the map. This can get you into trouble. (This would work on a compass rose on a nautical chart, since there the angle of the diagram is correct. However, on a USGS topo map, the angle on the diagram is schematic only.)

To various people who have commented on the amount of magnetic declination, and how fast it changes:
This really depends on where you are. For example in Chicago, declination is only 3 deg 28 min W, and is only changing by 5 min W per year. In Chicago you could probably ignore declination and get away with it for many purposes. However, where I live in Anchorage it is currently 18 deg 23 min E, and is changing by 18 min W per year. That means it changes by almost one degree every 3 years. Not a good idea to ignore it here.

To the original poster JeanetteIsabelle:
Don't let all these technical details scare you off. It really isn't that hard to aquire a basic working knowledge of navigation. Take it one step at a time. Use the old 'walk before you run' approach. Don't worry about a compass or GPS at first. Get your hands on a basic book, any of the several that have been recommended should be fine. Get a topo map of some area that you know well or that you plan to visit. Just start walking around, map in hand. You soon will develop a feel for how things are portrayed on the map vs the ground you are walking on. Ideally, find a place where you can get up high a bit and get a view of the surrounding area. The top of a hill, or even up a few floors on a building will work. Again, just start comparing map to terrain.

Once you have a basic feel for how things are portrayed on a map, then start thinking about learning how to use a compass. Again, just start simple, and work your way into more challenging situations. Here is where the book might be very helpful, or one of the free classes offered by REI or similar places.

Don't even think about getting a GPS until you have a good handle on basic map and compass stuff.

Besides a very useful skill, you will find that navigation can be a lot of fun for its own sake.

One other little tidbit about USGS maps and their idiosyncrasies. Natural features like land contours are printed in brown and water features (springs, creek, etc0 are printed in light blue. Cultural features (houses, roads, etc are often depicted in black. In using the map you will often find that the map was produced some twenty or thirty years ago. The result is that the natural features, brown and blue, are often very correct, while the cultural stuff is outdated - roads are built, cabins are torn down, etc. Maps get photo revised (the revision are depicted in purple), but even that doesn't happen consistently. The upshot is that you can rely on hills and crags being there, while the road or trail on which you are traveling may not be shown at all.

In my corner of the world, I used maps older that most of the members of this forum (made in 1943); the landscape was fine; roads, etc. were laughably inaccurate..

All this stuff about different datums is a bit arcane and technical. Its relevance depends a great deal upon the purpose for which you are using the map. If you are traveling and trying to reach the proper summit, pass, or drainage, it probably doesn't matter. If you are trying to located or find an archaeological site or fossil locality, it can be critical.

The thing about the different colors (red works its way into the scheme for showing dense urban areas) is that the USGS has good taste and the maps make great wall decorations - at least in my opinion. Others, like my wife, may not agree......

Very true. Also, the older the map, the more the magnetic declination will have changed. For general navigation you always want the most recent edition. When orienting a map, always look first to the big terrain features. Mountains typically don't change much. Manmade features change a lot with time.

Yes. You put it much more articulately than I did. Also, even at that datums are only important when working between paper map and GPS, or when using someone else's published waypoint. If you are only using your GPS, it doesn't really matter. For example, if you use your GPS to take a waypoint at your camp in the morning, your GPS can still lead you back to that camp at night, no matter what datum you use. Sometimes datums matter, but often they aren't that crucial.

True indeed. Long ago, I took a bit of cartography in college. The professor taught us that a good map is a thing of beauty. I still believe that. My home office has maps on the walls. However, I can't always convice my wife to put them up in the living room.

AKSAR, as a broad generalization, would it be safe to say that the further north (or south, if you are in the southern hemisphere), the more attention you should pay to magnetic declination and its rate of annual change. It seems pretty clear that the declination is more significant in Alaska than in Arizona. Is it just a matter of simple geometry?

JeanetteIsabel- have you got what you need?

Or do we need to continue debating how many angels can dance on the compass needle at its current declination? :-)

Hikermor,

Not quite simple geometry, but in a gross sense close. There is a line (in simple terms, which it is not) through the geographic north pole and the magnetic north pole (somewhere near Ellesmere Island) where the declination is 0. The closer you are to that line, the less of a problem you have. The greater your angle from that line the more the declination. Since the magnetic pole is in constant motion,the closer you are to the poles the faster the declination changes. If you are on the north end of Ellesmere your compass would point south if it could work.

Respectfully,

Jerry

Here is the declination map for the US in 2005