Determining the direction
A compass works according to the principle that the needle of the compass always points north. This allows you to calculate which direction you walk in. To facilitate that arithmetic, almost all compasses have a ring that can be rotated, so you can read in which direction you are walking.
In order to use a compass, you need a good map. This must be at least the north-south axis, so that you can decide for yourself where the north is indicated on the map.
If you have found this on the map, you can proceed as follows to determine your course:
Determine direction to the target
Place the compass on the map in such a way that its long side is over the axis from position (1) to destination (2). Make sure that the arrows point to the compass from position to destination and not the other way around.
North to determine the goal
Now press the compass firmly on the map as you rotate the ring. This rotates until the north-south axis of the ring runs parallel to the north-south axis of the map. Again, the N or 0 degrees pointing north at the ring should also point north to the map.
Determine course or direction of movement
Now take the compass in hand and keep it at eye-high. The compass must be held horizontally and the arrows on the plate must be pointed straight ahead. Now rotate with your body until the arrow of the ring points in the same direction as the needle of the compass. The (often) red end of the needle should now point in the same direction as the N or 0 degrees on the ring. The arrows on the plate now point in the direction you need to walk. Now, in the distant, find an object that the arrows point to and walk towards it. If you have arrived, repeat the previous steps and re-determine your direction.
The above sounds pretty simple and is in fact. It actually becomes difficult only when you actually want to (or should) measure very accurately. Then things like declination and misrepresentation are discussed.
Determining your position
Nothing is as annoying as not knowing exactly where you are on the map. However, if that is the case, you can use your compass and some landmarks in the area to calculate where you are. You’ll never really be able to calculate exactly where you are, but depending on the scale of your card, you can still draw on the map where you stand with an accuracy of several tens of meters.
To calculate your own position, we can use two different methods:
- cross measurement (the intersection of two different lines)
- triangular measurement (the intersections of three lines form a small triangle)
Cross measurement is the easiest of the two, simply because it takes less work and time. This method is often also slightly less accurate than the triangulation. For a cross measurement, you look for two recognizable (and known on the map!) objects in the area that are so apart that the angle between them is between 45° and 135°. At an angle smaller or larger, the method becomes less accurate.
First, determine the direction angle to the first object. You do this by pointing the compass at the object and then turning the compass rose around in such a way until the north of the rose is exactly the same as the north that indicates your compass needle.
Then place the compass on the map and rotate the compass until the lines of the compass rose run parallel to the lines to the (magnetic) north of the map. Now you make sure that your compass house or compass plate is against the object you just probed so you can draw a straight line from that object to the direction you are.
Now you do the same with the other object: gauge and measure angle, transfer angle to the map, and then draw a line.
You’ll see that the two lines are cutting each other somewhere: this is where you’re about to be.
With a triangulation you do exactly the same as with the cross measurement, only you now use three objects and therefore three lines. Where the lines intersect, a very small triangle is often created, hence the name triangulation. You’re in the middle of that triangle.
As you know, the needle of the compass always points north. What you probably didn’t know is that this isn’t the real north. In reality, there are three different ‘north’:
This is the real north as it always appears on a globe, namely the tip of the globe. This place is a fixed place and has once been established using complex calculations. Now you could find the geographic north pole more easily by means of a GPS. On a map, the geographical north is usually indicated by a star (*).
This is the north your compass needle always points to. It is a place somewhere north of Canada where there is such a magnetic force field that it is always found by the compass needle. In reality, the compass needle is consistent with a certain flow of magnetic forces, and they always point in the direction of that place: the magnetic north. Problem of this magnetic north is that it is not always in the same place. Because the magnetic force fields are always in motion, the magnetic north always moves a little. That’s why your compass always points in a different direction (this difference is not visible to the naked eye because the change per year often amounts to only less than 1 degree). On maps, the magnetic north is usually indicated by a (half) arrowhead.
This, too, is a changing north, which is what the map maker has chosen as a north. Often this coincides with the geographical north, but for technical reasons there are also many cartographers who choose to set up a so-called map north themselves. The difference between the geographical north (i.e. that of the globe) and the magnetic north (which indicates the compass) is called declination. And because the different magnetic force fields on the globe are constantly changing, so the declination changes a bit every year. This change is always indicated on a map when drawing declination and misgiving which is explained in the chapter on misorientation.
In the drawing below you can see what the declination fields looked like in 1996.
The Netherlands is almost exactly on the 5° line and therefore the declination in the Netherlands is about 5°. Better compasses give you the ability to eliminate the declination by adjusting the degree ring to the size of the declination. You should then take into account that a western declination is often displayed with a negative value, while an eastern declination is often displayed with a positive value.
If you don’t take into account the declination in a given area, this can result in you being able to get off course as much as 45° if you don’t pay close attention to where your compass is pointing. So it is always important to look closely at the map north, where the geographical north is located and where they are both relative to the magnetic north. This kind of thing is usually displayed on a map with a special drawing that is explained in the piece on misrepresentation.
Disalignment is a term that is often (usually) swapped with declination. It is quickly said that the declination of a particular map is x degrees or minutes, but then one almost always talks about the misalignment. Misalignment and declination are only the same on maps where the map north and the geographical north are the same.
Misalignment occurs because there is a difference between the different north, as explained in the chapter on declination. Because a cartographer chooses a fictitious point as north, a difference arises between the north as our compass points and the north as indicated on the map.
Declination and misordination are usually indicated on the map by a drawing similar to the drawing next to it. The different north are indicated by their abbreviations and symbols (star for geographical north and half arrowhead for the magnetic north). In addition, there are different angles at the lines to indicate the extent to which the different north differ from each other. Please note that these drawings (virtually) are never truthful – i.e. with the right angle – but that it is purely schematic to show how the different north relates to each other. In addition, this data is displayed for the center of the map. Finally, it still needs to be added to when this data applies and what the annual change is (i.e. how much the declination increases or decreases per year).
If we now take the secondary drawing as an example, we can see 3 different numbers:
This is the misgiving (relative to the map!), namely the difference between the map north and the magnetic north.
This is the deviation between the map north and the geographical north.
This is the declination, namely the difference between the geographical north and the magnetic north.
The quick ore will soon see that the misorientation consists of a sum of declination and the deviation between the map north and the geographical north.
Misgiving to the present
Let’s now say that the map also states that the declination decreases by 7′ (7 minutes) each year, and that the data on the map applies for the year 2007, then you can calculate that the figures for now (2010) respectively: 3°57′ (4° 18′ – 3 times 7′) ) , 1°27′ (the difference between the north map and the geographical north does not change) and 2°30′ (the difference between the two previous figures). Useful to know when making this calculation is that there are 60 minutes going in one degree. With the above knowledge you can calculate more truthful angles with your compass and therefore work even more accurately. How to do that is explained in the chapter on the conversion of the misthof.
Miscalculation (by map or terrain)
Miscalculate from the map to the compass/surroundingarea
Now that you know that there is a difference between the north that you used earlier and the north that you actually need to use you can be more accurate in determining the direction to walk. To do this, however, you have to understand the logic of the correction that you have to apply to the measurements you take on the map. Therefore, an easy example: set the angle of the map north and the place you want to go is 326° (always count clockwise, so this is towards the northwest) compared to the map north. You know, however, that the magnetic north (which indicates the compass) is 3°57′ west of the map north. This means that the angle on your compass should be 326° PLUS 3°57′ (330°).
Side-by-side drawing is likely to make this clearer:
The angle you measure on the map is shown by the grey plane, because this is the angle between the map north (KN) and the target direction (DR) of your destination.
However, if you correct the misdrooling at this measured angle, you will see the angle represented by the green plane (the difference between the magnetic north (MN) and the target direction (DR).
Set this angle on your compass and turn around (with the compass in hand) until the red tip of the compass needle points exactly the same direction as the north indicating your compass rose. The arrow on your compass will then point out which direction to take.
From the above you can therefore see that if magnetic north is west of the map north, you have to add the misgiving at the angle you measured on the map. If the magnetic north lies east of the map north, then the misgiving must therefore be pulled off.
Miscalculate from the compass/environment to the map
To calculate the angle you measure with your compass to the corner you need to use on your map, you work the other way around.
Side-by-side drawing is likely to make this clearer:
The angle you measure with your compass is represented by the gray plane, because this is the angle between the magnetic north (MN) and the target direction (DR) of your destination.
However, if you correct the misdrooling at this measured angle, you will see the angle represented by the green plane (the difference between the map north (KN) and the target direction (DR).
By now setting this new-found angle on your compass and then placing the compass on the map (north of the compass rose similar to the north of the map!), you can calculate how the line from your destination should run to your current position.
You have just seen that the rule previously used to convert the map angle to the compass angle is exactly the other way around when it comes to a compass angle that you convert to a map angle: if magnetic north is north of the map, you need to subtract mis-ordination from the angle you measured with your compass. If the magnetic north lies east of the map north, the misdirection should be added to the angle you measured with your compass.
Have you taken all things into account (declination, misrepresentation, etc.) your compass doesn’t seem to work properly if you want to use it in Africa or Australia. That’s right, because there’s something else you have to take into account: inclination.
Inclination is hephenomenon that ensures that your needle never stays completely horizontal. That would only be the case if the magnetic force that attracts the needle is at exactly the same height. But, as you understand, it’s not, so your needle is always slightly pulled down.
Fortunately, in the Netherlands (and almost the entire rest of Europe) it has little or no effect on your measurements. After all, the needle does not touch the top or bottom of the compass house and will therefore simply be able to rotate freely. In other parts of the world, however, it is indeed a problem and the needle cannot spin freely in the compass house and is therefore hindered in pointing out the north. The strength of this force (thus inclination) is divided all over the world into 5 zones, each with a certain strength of inclination. In the drawing below you can see how these zones are divided around the world.
However, manufacturer Recta has other areas, simply because Recta only uses two inclination zones (northern hemisphere and southern hemisphere).
To prevent (or reduce its effect) you can do different things. For example, an often applied solution is to see what the angle of the inclination is and then keep your compass at the same angle so that the needle can still rotate freely. The problem is, however, that you will then have to deal with a different force: gravity. It will therefore also pull on the compass needle (on the side that points most to bends of course) and thereby influence the measurements. Another solution is for every inclination zone you visit to purchase the compass created for it. But this is a rather expensive solution, especially if the visits are only one-off.
My advice is therefore to buy a compass that does not care about inclination. Nowadays there are compasses that do not care about inclination. This can be done by separating the magnet and the needle so that the needle has no problem with inclination.