Mag north... Why?

[FiddleCaver]

I dunno anyone who uses a compass (surveying not included) while in a cave.

I've been known to bust out a compass while not surveying, mostly when looking for connections or in unmapped portions. At no point however have I ever thought to myself, well North is actually over here to the left a little.

I think that this is pretty pointless, myself. I could see maybe if your cave was in some region where North was actually like 10+ degrees from Nmag, but then really, those people who cave where the compass doesn't point N should understand that and be used to compensating for it.

[cavedoc]

Several of us are having a discussion about why magnetic north needs to be shown on a cave map.

Because it looks prettier that way? Serously. As everyone else has pointed out, we don't NEED it. And it can become meaningless with the years. But a plain north arrow, probably pointing straight up anyway, is just boring looking. And you wouldn't want the cart. salon judges be bored when they looked at your map.

[John Lovaas]

I dunno anyone who uses a compass (surveying not included) while in a cave.

Ummm... anytime I use a map in a cave? Maybe I am a Luddite, but whenever I use a map, I orient it- and that requires a compass.

And the battered little Silva in my cave pack can be useful on the surface as well.

As to the grid north/magnetic north debate, I don't think it hurts to include both, as long as include the metadata for the Nm arrow.

In my limited experience, the printed map is often the only surviving artifact of past survey efforts. While we'd like to think that grotto libraries and state surveys are perfect systems for retaining data, they are not. Because of the (generally) wider distribution of cave maps, they have a better chance of making it into the hands of users in the future than the source data.

Now the value of including the Nm arrow is also dependent on where you are in the US; most everything I draft is within a 1 to 1.5 degree window, which is within the accuracy tolerance of the individual survey shots. So if my survey is no more accurate than the range of grid north/Nm, then why bother, I guess?

I reckon that whatever North arrow(or arrows) you use, it should be clear to the user just which North it is. 30 or 40 years down the road, it just might be of value to a researcher- and if the magnetic north pole continues to move faster each year, the datum information may be even more important.

[Jeff Bartlett]

I dunno anyone who uses a compass (surveying not included) while in a cave.

Ummm... anytime I use a map in a cave? Maybe I am a Luddite, but whenever I use a map, I orient it- and that requires a compass.

it sounds like you're using maps that don't have a north arrow at all. which i don't recommend.

[Eric Wright]

I dunno anyone who uses a compass (surveying not included) while in a cave.

Ummm... anytime I use a map in a cave? Maybe I am a Luddite, but whenever I use a map, I orient it- and that requires a compass.

it sounds like you're using maps that don't have a north arrow at all. which i don't recommend.

I don't think that's what John is suggesting. "Orient a map" means to physically rotate it so that North on the map is aligned with North on the ground (or Nm on the map is aligned with the direction your compass needle points) so that the drawing of the passage you are in trends in the same direction of the actual passage. You'd need a North arrow on your map to be able to do that.

[John Lovaas]

"Orient a map" means to physically rotate it so that North on the map is aligned with North on the ground (or Nm on the map is aligned with the direction your compass needle points) so that the drawing of the passage you are in trends in the same direction of the actual passage. You'd need a North arrow on your map to be able to do that.

Thank you for clarifying that point, Eric. I'm from another century

That's right, you young whippersnappers- once upon a time all we had to navigate around the world with were these pieces of paper, and we had little magnetic doohickies that pointed towards a big chunk of iron up around Hudson Bay that we used to point the maps in the right direction

I'll apologize in advance if I ever use Fibber McGee's Closet as an analogy for anything. Just call me Grandpa Simpson from now on.