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    Compass directions and "North by Northwest"
    From: Frank Reed
    Date: 2012 Feb 12, 21:01 -0800

    Everyone knows the standard intermediate compass directions like NNE, NE, ENE, and so on, but the "by" directions are a bit of a mystery. Here's my easy way to work them out.

    First, between each pair of standard compass directions, there is one and only one "by" direction. Between North and North-northwest you'll find "North by East" usually written NbE. Second, the names for the by directions always follow one of two patterns: XbY or XXbY. That is, the second part is always a cardinal point, and the first part is never three letters. That rule excludes both NbNW (the title of a legendary Hitchcock film) and NNEbNE as valid compass directions. Though these "off-rule" names can be unambiguously converted to a bearing, they're not on the standard list. There's one more rule which is almost too obvious to mention: the Y direction is always within 90 degrees of the X/XX direction. That excludes combinations like NEbS or, even worse, NbS.

    Next, the "by" directions are 11.25 degrees (45/4) away from the first direction in the formula and towards the second direction in the formula. I have found that an easy way to remember this is to read the "b" or "by" as "and a bit" or "and a bit towards" remembering that this "bit" is 11.25 degrees which is near enough to 10 degrees for most purposes. So NbE or "north by east" can be read as "north and a bit east". To find this direction, you face north and then look about 11 degrees towards the east from there. The exact bearing is 011.25 degrees.

    Suppose you're asked to name the compass direction halfway between NW and NNW. You know that it has to start with one of those directions, but the pattern does not allow "three letter" directions, so we have to start with NW. From there we're turning a bit towards the north. So the correct "by" direction is NWbN or "Northwest by North". And if you want the numerical bearing, since NW is 315 degrees, NWbN is 326.25 degrees. To me the key to making all of this 'easy' is translating "by" as "and a bit".

    Why bother? It makes you saltier! And you can read more historical documents, too.


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