# Boyscouts: Explain compass terminology **URL:** \ **Category:** Factual Questions\ **Created:** [March 15, 2000, 1:08pm UTC](https://boards.straightdope.com/t/boyscouts-explain-compass-terminology/8700 "2000-03-15T13:08:00Z")\ **Posts on this page:** 18\ **Page:** 1
**Author:** ![Jinx](https://avatars.discourse-cdn.com/v4/letter/j/c6cbf5/32.png) [@Jinx](https://boards.straightdope.com/u/Jinx)\ **Post date:** [March 15, 2000, 1:08pm UTC](https://boards.straightdope.com/t/boyscouts-explain-compass-terminology/8700/1 "2000-03-15T13:08:00Z")
Can someone please explain the difference between the following phrases when expressing direction? a) Northwest b) North by Northwest c) North of Northwest d) North-Northwest At first, one might think these are simply different ways of expressing the same direction. But, they appeared in a list describing the location of the “population center” of the US since 1790. {I WAG that these might have specific meanings if degrees were specified, such as 3 degrees north of northwest. Using a pilot’s convention that 0 degrees is North, and West is typically accepted as 270 degrees; my example would translate to 273 degrees on a compass?} * * * “They’re coming to take me away ha-ha, ho-ho, hee-hee, to the funny farm where life is beautiful all the time… :)” - Napoleon IV ---
**Author:** ![C\_K\_Dexter\_Haven](https://avatars.discourse-cdn.com/v4/letter/c/b2d939/32.png) [@C\_K\_Dexter\_Haven](https://boards.straightdope.com/u/C_K_Dexter_Haven)\ **Post date:** [March 15, 2000, 1:40pm UTC](https://boards.straightdope.com/t/boyscouts-explain-compass-terminology/8700/2 "2000-03-15T13:40:00Z")
North by northwest is from Hamlet, describing his madness. … or from Alfred Hitchcock, with Cary Grant, Eva Marie Saint, and James Mason, _inter alia._ ---
**Author:** ![RM\_Mentock](https://avatars.discourse-cdn.com/v4/letter/r/e274bd/32.png) [@RM\_Mentock](https://boards.straightdope.com/u/RM_Mentock)\ **Post date:** [March 15, 2000, 2:04pm UTC](https://boards.straightdope.com/t/boyscouts-explain-compass-terminology/8700/3 "2000-03-15T14:04:00Z")
> [@](#): > > Originally posted by Jinx: > **I WAG that these might have specific meanings if degrees were specified, such as 3 degrees north of northwest. Using a pilot’s convention that 0 degrees is North, and West is typically accepted as 270 degrees; my example would translate to 273 degrees on a compass?** But Northwest would be halfway between North and West, so 3 degrees north of northwest is 318 degrees. Without referring to any “official” list, here’s how I interpret those directions: a) Northwest = 315 degrees (halfway between N and W) b) North by Northwest = I always thought this was the same as d), but now I’m not sure. c) North of Northwest = 315-337.5, exclusive d) North-Northwest = 337.5 (halfway between N and NW) So, most are different. * * * rocks ---
**Author:** ![tomndebb](https://avatars.discourse-cdn.com/v4/letter/t/b9e5f3/32.png) [@tomndebb](https://boards.straightdope.com/u/tomndebb)\ **Post date:** [March 15, 2000, 2:33pm UTC](https://boards.straightdope.com/t/boyscouts-explain-compass-terminology/8700/4 "2000-03-15T14:33:00Z")
It’s really more of a nautical experience than a boy scout adventure. Back before everyone went to 360° numeric notation, ships compasses were laid out over a card with 32 points on it. N E W S = 4 points then the points halfway between N E S W, NE SE SW NW, give four more points halfway between each of those eight points are NNE ENE ESE SSE SSW WSW WNW NNW giving us a total of 16 points Those points were, in turn, divided to give up 32 points on the compass. The last 16 points are: (between N and NNE) North by East (between NNE and NE) Northeast by North (between NE and ENE) Northeast by East (between ENE and E) East by North (and I’m not about to type out all of them) So, for one quarter of the compass, the directions are: North, North by East, North Northeast, Northeast by North, Northeast, Northeast by North, East Northeast, East by North, East Of course, 32 points don’t give you really close sailing instructions, so each point is further divided into quarters, giving 128 points or quarter points on a compass, a quarter point being a little less than 3° on a 360° compass. ## Further information can be found at [http://www.mcallen.lib.tx.us/staff/compcrd.htm](http://www.mcallen.lib.tx.us/staff/compcrd.htm) and at [http://www.ukans.edu/~kansite/ww\_one/naval/boxco000.htm](http://www.ukans.edu/~kansite/ww_one/naval/boxco000.htm) (although why the University of Kansas is sporting nautical information, I don’t know). Tom~ ---
**Author:** ![InutilisVisEst](https://avatars.discourse-cdn.com/v4/letter/i/d2c977/32.png) [@InutilisVisEst](https://boards.straightdope.com/u/InutilisVisEst)\ **Post date:** [March 15, 2000, 4:27pm UTC](https://boards.straightdope.com/t/boyscouts-explain-compass-terminology/8700/5 "2000-03-15T16:27:00Z")
Just to chime in with the Boy Scout viewpoint – we never got past the 16 points, and then only for general information. In general, degrees ruled. The military also uses “mils,” of which there are 6400 in a complete circle. * * * Sure, I’m all for moderation – as long as it’s not excessive. ---
**Author:** ![tomndebb](https://avatars.discourse-cdn.com/v4/letter/t/b9e5f3/32.png) [@tomndebb](https://boards.straightdope.com/u/tomndebb)\ **Post date:** [March 15, 2000, 10:07pm UTC](https://boards.straightdope.com/t/boyscouts-explain-compass-terminology/8700/6 "2000-03-15T22:07:00Z")
Ahhhhrrrgghhh! That _should_ have been: North, North by East, North Northeast, Northeast by North, Northeast, **Northeast by East** , East Northeast, East by North, East ---
**Author:** ![Ursa\_Major](https://avatars.discourse-cdn.com/v4/letter/u/a88e57/32.png) [@Ursa\_Major](https://boards.straightdope.com/u/Ursa_Major)\ **Post date:** [March 15, 2000, 10:44pm UTC](https://boards.straightdope.com/t/boyscouts-explain-compass-terminology/8700/7 "2000-03-15T22:44:00Z")
BTW- The sixteen points make up what salts like to call a “windrose”. ---
**Author:** ![CurtC](https://avatars.discourse-cdn.com/v4/letter/c/ce73a5/32.png) [@CurtC](https://boards.straightdope.com/u/CurtC)\ **Post date:** [March 15, 2000, 11:28pm UTC](https://boards.straightdope.com/t/boyscouts-explain-compass-terminology/8700/8 "2000-03-15T23:28:00Z")
> [@](#): > > CKDextHavn wrote: > North by northwest is from Hamlet, describing his madness. > … or from Alfred Hitchcock, with Cary Grant, Eva Marie Saint, and James Mason, inter alia. Trivia: the “North by Northwest” in the movie is a joke. Check out which airline Cary takes from Chicago to South Dakota. ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [March 15, 2000, 11:33pm UTC](https://boards.straightdope.com/t/boyscouts-explain-compass-terminology/8700/9 "2000-03-15T23:33:00Z")
In the old days of sail, one of the first things sailors had to learn was to recite in order all the points of the compass and that was called “boxing the compass” Also remember the compass does not point to the true geographic North, or even necessarily to magnetic north. The difference between true and magnetic north is called variation and changes with place and time. The difference between compass and magnetic is called deviation and is specific to ship and compass. most of it can be corrected with small magnets (flinders bars) but the remainder must be accounted for and is variable with heading. these corrections are labeled E or W depending on direction. When I learnt how to go from one to the other I learnt a mnemotechnic aide: True + Variation = Magnetic + Deviation = Compass (add West, subtract east) True Virgins make Dull Companions (at Weddings) There was a similar phrase to go in the other direction but I cannot recall it now For a good discussion of these things check out Bowditch, American Practical Navigator volume I, published by the Defense Mapping Agency. Another last point: the earth’s magnetic field is more horizontal at the equatorial regions but gets progressively more vertical nearer to the poles and a compass will become almost useless near the magnetic poles. Boat’s compasses are made for different regions as a compass that is made for tropical regions will not work so well in very northern latitudes and vice versa. ---
**Author:** ![Billdo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/billdo/32/315_2.png) [@Billdo](https://boards.straightdope.com/u/Billdo)\ **Post date:** [March 15, 2000, 11:56pm UTC](https://boards.straightdope.com/t/boyscouts-explain-compass-terminology/8700/10 "2000-03-15T23:56:00Z")
To fill out the already complete information tomndebb and everyone else has provided, the following is how quarter points go: north north 1/4 east north 1/2 east north 3/4 east north by east north northeast 3/4 north north northeast 1/2 north north northeast 1/4 north north northeast north northeast 1/4 east north northeast 1/2 east north northeast 3/4 east northeast by north northeast 3/4 north northeast 1/2 north northeast 1/4 north northeast (and so on . . . .) ---
**Author:** ![Olentzero](https://avatars.discourse-cdn.com/v4/letter/o/90ced4/32.png) [@Olentzero](https://boards.straightdope.com/u/Olentzero)\ **Post date:** [March 16, 2000, 3:49pm UTC](https://boards.straightdope.com/t/boyscouts-explain-compass-terminology/8700/11 "2000-03-16T15:49:00Z")
It doesn’t get as detailed as **Billdo** ’s entry, but this gives you a pretty good idea: [http://www.ctmap.com/gisnet/notebook/comprose.html](http://www.ctmap.com/gisnet/notebook/comprose.html) ---
**Author:** ![CurtC](https://avatars.discourse-cdn.com/v4/letter/c/ce73a5/32.png) [@CurtC](https://boards.straightdope.com/u/CurtC)\ **Post date:** [March 16, 2000, 4:44pm UTC](https://boards.straightdope.com/t/boyscouts-explain-compass-terminology/8700/12 "2000-03-16T16:44:00Z")
> [@](#): > > sailor wrote: > Also remember the compass does not point to the true geographic North, or even necessarily to magnetic north. As an example, here in Dallas, Texas, the compass points six degrees to the East of true North, but the north magnetic pole is actually two degrees _West_ of true North. ---
**Author:** ![RM\_Mentock](https://avatars.discourse-cdn.com/v4/letter/r/e274bd/32.png) [@RM\_Mentock](https://boards.straightdope.com/u/RM_Mentock)\ **Post date:** [March 16, 2000, 5:05pm UTC](https://boards.straightdope.com/t/boyscouts-explain-compass-terminology/8700/13 "2000-03-16T17:05:00Z")
CurtC, sailor That two degrees is neither variation nor deviation, right? It’s just ignored, as the compass magnetic north is a local magnetic north, rather than the real magnetic “north” pole. * * * rocks ---
**Author:** ![Jinx](https://avatars.discourse-cdn.com/v4/letter/j/c6cbf5/32.png) [@Jinx](https://boards.straightdope.com/u/Jinx)\ **Post date:** [March 16, 2000, 5:56pm UTC](https://boards.straightdope.com/t/boyscouts-explain-compass-terminology/8700/14 "2000-03-16T17:56:00Z")
> [@](#): > > Originally posted by RM Mentock: > **…local magnetic north, rather than the real magnetic “north” pole.** Local magnetic north? Huh? 😕 RM Mentock, you lost me! Did you perhaps mean to say “magnetic north” vs. “geographic north”? ## Somebody set me straight, here! “They’re coming to take me away ha-ha, ho-ho, hee-hee, to the funny farm where life is beautiful all the time… :)” - Napoleon IV ---
**Author:** ![Ursa\_Major](https://avatars.discourse-cdn.com/v4/letter/u/a88e57/32.png) [@Ursa\_Major](https://boards.straightdope.com/u/Ursa_Major)\ **Post date:** [March 17, 2000, 6:07am UTC](https://boards.straightdope.com/t/boyscouts-explain-compass-terminology/8700/15 "2000-03-17T06:07:00Z")
There is such a thing as local magnetic fields. I don’t know what causes them (iron deposits?) but you are warned about them in any navigation class you might take. Compasses are very imprecise instuments for navigation. When using a compass alone to plot a course, it is known as “dead reckoning” which is about half a step above “guessing”. I use dead reckoning for short trips to Catalina or the Channel Islands (Hell, half the time you can see them from the coast). No matter how well you keep the needle on your desired course, you never end up exactly where you predict. Most of this is due to things like current, but the overall inaccuracy of the compass, also plays a role. ---
**Author:** ![InutilisVisEst](https://avatars.discourse-cdn.com/v4/letter/i/d2c977/32.png) [@InutilisVisEst](https://boards.straightdope.com/u/InutilisVisEst)\ **Post date:** [March 17, 2000, 6:18am UTC](https://boards.straightdope.com/t/boyscouts-explain-compass-terminology/8700/16 "2000-03-17T06:18:00Z")
The difference between G.N. (geological North) and M.N. (magnetic North) is called declination. At the bottom of USGS maps there’s a little declination diagram valid for the center of the map. I’m pretty sure that “magnetic North” refers to where your compass points when you’re standing there, taking into account local weirdness as well as the Earth’s magnetic poles. ---
**Author:** ![RM\_Mentock](https://avatars.discourse-cdn.com/v4/letter/r/e274bd/32.png) [@RM\_Mentock](https://boards.straightdope.com/u/RM_Mentock)\ **Post date:** [March 17, 2000, 6:47am UTC](https://boards.straightdope.com/t/boyscouts-explain-compass-terminology/8700/17 "2000-03-17T06:47:00Z")
Jinx It’s like InutilisVisEst says, there is local weirdness. It’s not just magnetic mountains, sometimes the differences in the magnetic field are embedded deep in the earth. The Earth is approximately like a big bar magnet, but not quite. Notice what CurtC says, the compass in Dallas points east of north, when the actual ‘north’ magnetic pole (actually a south pole, heh) is west of north. * * * rocks ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [March 17, 2000, 1:47pm UTC](https://boards.straightdope.com/t/boyscouts-explain-compass-terminology/8700/18 "2000-03-17T13:47:00Z")
## FWIW, I just pulled out the L.A. sectional chart. The isogonic line nearest to where I live shows 14 degrees of deviation between magnetic north and true north. The Seattle sectional shows local magnetic distrbances in certain areas. Engines, radios, etc. also affect the compass. “I must leave this planet, if only for an hour.” – Antoine de St. Exupéry Are you a turtle?