Compasses

COMPASS AND MAP TOGETHER

The compass needle points to geographic North only at the agonic line (line of no declination because it is the same as the geographical North line). This line passes now through the west part of Florida and the Great Lakes. My friends in Wisconsin never have to adjust for magnetic declination. I hike and hunt in New York, where I have to adjust for 17 degrees West, and in Maine as much as 22 degrees West. The people on the West coast have to adjust for declination East.
If you are located over that line, the needle will point geographic North. All other times the magnetic needle points to the magnetic North that is located some 1300 miles from the geographic North.
Your topographic map will tell you in a diagram found in the left corner how much is the declination in your area. If the map is old, you may have to find the present declination to be more accurate in your traveling if it involves a long trek, where one degree could make a difference.

Once you found how many degrees of declination you have to adjust for, you can do it on the compass or on the map.

PICTURE OF A COMPASS WITH INSIDE DECLINATION SCALE



PICTURE OF A COMPASS WITH AN ADJUSTABLE SCALE, IT MOVES THE LOWER INSIDE DIAL
BY A GEARED SCREW.

PICTURE OF A COMPASS WITHOUT A SCALE, IN THIS CASE YOU HAVE TO FIGURE YOUR DECLINATION BY ADDING OR SUBSTRACTING FROM THE 360 DEGREES, IN THIS CASE THE DECLINATION IS 18 WEST, SO THE NEEDLE IS PLACED OVER THE 342 MARKINGS.
EACH OF THE MARKINGS IS EQUIVALENT AT 2 DEGREES, THERE ARE 180 OF THEM AROUND THE COMPASS.



ADJUSTING THE MAP
To make the map speak compass language (magnetic North), extend the line of declination all across the map from the little diagram in the corner, using a long ruler and spacing the lines about two inches. Or use your compass as a protractor (measuring angles) to trace the start of the line from anywhere on the map.
After doing this, both the compass and the map will “speak” magnetic readings and you will not have to adjust the compass for magnetic declination.

ADJUSTING THE COMPASS
If you would rather adjust for declination on the compass (and save yourself from tracing lines on the map), every time you are going to follow a bearing in the field, you have to move the needle to the proper declination. So instead of pointing to North, it will point 22 degrees West of North (in the case of Maine), or 338 degrees.
Or, if you are West of the agonic line, then your declination will be East and you will have to move the needle East of the North marking on the compass.
Some compasses have a scale printed in the capsule, and some of them adjust by means of a internal rotating bezel that adjusts with a screwdriver stored in the lanyard. I like the latter type because there is nothing to do after you set it; you just place the needle in the “gate” that is already adjusted to the proper declination after you do it the first time.

To use the compass and map together, find where you are in the map and where you want to go, connect the two places with a line that extends from the side of your compass, and without moving it, rotate the “capsule” of the compass so that the lines inscribed on the bottom of the capsule combine with your drawn magnetic lines on the map OR the North line(s) or margin on the map if you are adjusting for declination on the compass.

Just follow the bearing that you have just set at the back end of the “line of travel arrow” and you will arrive at your destination.

IN THIS PICTURE, A SUUNTOO S5SK IS USED TO CONNECT THE START AND FINISH, ONLY THING TO DO NOW IS ROTATE THE CAPSULE UNTIL THE LINES INSCRIBED IN IT, PARALLEL THE NORTH LINES ON THE MAP, AND READ THE DEGREES AT THE JUNCTION OF THE LINE OF TRAVEL ARROW AND THE BEZEL WITH THE NUMBERS. (DISREGARD THE MAGNETIC NEEDLE WHEN THE COMPASS IS ON THE MAP)



All this is very basic, but it will take you to the proper destination. If you would like to study map and compass a little more and learn how to navigate using more elaborate techniques, such as using handles, taking triangulation, or navigating in open terrain without the use of landmarks, I recommend you buy one of the books that are available on the subject.

I started many years ago with the classic “Be Expert with Map & Compass” by Bjorn Kjellstrom, which I recommend, but there are many other books that you can get from places like REI.
Using Map and Compass by Don Geary
The Outward Bound Map and Compass handbook by Glenn Randall
Wilderness Navigation by Bob and Mike Burns

I hope this little post can help someone interested in navigating the woods by map and compass. I feel that is a great need to go back to the basics to supplement and complement navigation with GPS, that after all, being electronic and depending on batteries can fail us when most needed.

Best wishes
Watchmaker

MAP COMPASS AND GPS
USING THE UTM GRID

A GPS is a great navigation tool. Among others things it can tell where you are on hearth which was the main concern for earlier navigators of the Spanish and Portuguese navies, until reliable navigation tools such as the sextant were invented.
Land navigation and exploration was also the province of the sextant; it was used in the jungles with an artificial horizon (a separate glass case containing mercury), and the star to drop down was the sun, as the readings were taken during the day as tree canopy made night reading almost impossible.

Today a small gadget called GPS can do the same for us in only a few minutes. The tool can give us our position on a map using Latitude and Longitude, UTM, military grid, or user grid.
It can do this during the day or night, with clouds or storm, best of all the GPS can fit even in a small pocket, the new units are more accurate than ever and can pin point your position with an accuracy of a few feet.
This position can be plot in a topographic map if you have a latitude/longitude ruler or even eyeballed, if the map is provided with a UTM grid or military grid.

Most new topographic maps now are provided with an UTM grid (Universal transverse Mercator) which is based on the metric system. In this system the latitude is measured in meters north or south of the Equator, and the longitude from meters from the center of a zone, of course the names change and the longitude is called Eastings and the latitude Northings.





In our map you can see an X named start and another X named finish. The place marked finish is where we left the quads on the side of the trail to climb up to Blenheim Hill early that morning. The purpose was to check the creek for trout and scout the area adjacent to the top of the hill.

The reading on the GPS for the place where we left the quads, was 4.700.200 meters North (you use the margin of the map scale) and 541,100 meters East from zone 18 (you use the scale in the top of the map). The first two numbers are the Zone and do not count as meters.
As we had spent two days using the GPS on others locations the gadget was getting very low on battery juice, so we decided to navigate by compass and save the batteries to take readings of the position of interesting places only.

By the end of the day and very tired we found ourselves near the unimproved road that lead to the road next to the cemetery. A reading of our position with the GPS using the UTM system indicated that we were 4,700.000 meters north of the Equator and 539,400 meters east of the zone 18, (see how easy is to count meters in the 1,000 squares with the tick’s marks in the margin of the map counting for 100 meters each).

Tracing a line from start to finish and measuring the degrees with the compass (used as a protractor and disregarding the magnetic needle) gave us a direction to go 80 degrees and 1700 meters for distance, (but the GPS already told us that).
The trek was on okay -terrain slopping downhill and we had to be careful with our footing only in the last 350 meters downhill to the quads.

The other option was to take the road going to the one near the cemetery (1300 meters) walk on that road passing by the ruins of the School until the next trail left (1900 meters) and walk uphill about 1,000 meter to the quads, a total of 4,200 meters.



In a heavy forest with no landmarks and not elevation to take triangulations readings with a compass, it is impossible to know where you are, the GPS can give you your exact position day or night and you can plot that position in the map using the Universal Transverse Mercator grid.

You can do that also with the Longitude and Latitude, but you have to prepare your map (with a different grid) and have a latitude and longitude ruler to measure your position. As GPS’s are easily adjusted for the UTM grid, it is the most convenient and easiest to use of all the grids.


In this explanation we have used the three tools to complement each other, the map, GPS and compass, and demonstrated that finding a road at the end of the day, it is not the shortest route for traveling to your destination; it also demonstrated that you don’t have to be glued to your GPS (as I see many people in the woods doing) to get your money worth out of the gadget.
Best wishes


Watchmaker