The location is 1.379 inches North of coordinate line 37 degrees 47 minutes and 30 seconds. The North designation means that we will use the 19.8 seconds per inch figure and it also means we will add the number of seconds we get, to the value of the coordinate line. 1.379 inches x 19.8 seconds per inch = 27.3042 rounded off to 27 seconds. Now, we add the 27 seconds to the value of the coordinate line. 37 degrees, 47 minutes and 30 seconds + 27 seconds = 37 degrees, 47 minutes and 57 seconds. If your GPS displays in degrees, minutes and seconds, that is your coordinate. However, if your GPS displays in degrees, minutes and thousandths of a minute, you will need to divide your number of seconds by the number 60 to convert your seconds to thousandths of a minute. In this case the coordinate would be 37 degrees 47 and nine hundred and fifty thousandths of a minute, or N37°47.950'.
The location is 1.823 inches West of coordinate line 83 degrees, 32 minutes and 30 seconds. The West designation means we will use the 24.5 seconds per inch figure and we will add the number of seconds we get, to the value of the coordinate line. So, 1.823 x 24.5 seconds per inch = 46.4865, rounded off to 46 seconds. Add this to the value of the coordinate line as--83 degrees, 32 minutes and 30 seconds + 46 seconds =83 degrees, 32 minutes and 76 seconds. Since there are only 60 seconds in one minute, this figure would convert to 83 degrees, 33 minutes and 16 seconds. Again, to convert the seconds to thousandths of a minute, divide the number of seconds by the number 60. In this case the answer would be 267 thousandths. So, the West coordinate would be W83°33.267'.
Therefore, the coordinate for the Swift-1949 survey mark is: N37° 47.950' x W83° 33.267'.
When you write down the distance and direction, of the location, from the coordinate line, if the direction is East or West, you will use the 24.5 seconds per inch figure, and if it is West of the coordinate line, you will add to the value of the coordinate line. If the location is East of the coordinate line, you will subtract from the value of the coordinate line to get the coordinate for your location.
When you write down the distance and direction, of the location, from the coordinate line, if the direction is North or South,, you will use the 19.8 seconds per inch figure. If the direction is North, of the coordinate line you will add to the value of the coordinate line and if the direction is South of the coordinate line, you will subtract from the value of that coordinate line to get the coordinate for the location.
When measuring something in thousandths of an inch, it is difficult to get the same measurement twice. If this happens, don't worry. You can be off a few thousandths of an inch or a few thousandths of a minute when you figure your coordinate and still be just fine. One point to remember is that if you travel a distance of one mile with a one degree error in your navigation, you will still only be about 92 feet off course. It is always good to be careful and most GPS units come with the warning, "don't use that unit as your only means of navigation." If you are careful in your coordinate calculations, become fairly proficient with map and compass and pay attention to detail, you will be able to use these instructions anywhere your GPS unit will function, to find your way to and from any area on the USGS maps, even if you have never been to these areas before. I have done this myself, and I can say with confidence, this method of finding coordinates is sufficiently accurate, for this application. I use this method along with my Eagle brand Accunav Sport GPS unit, USGS 7.5 minute quadrangle maps and a Silva, Ranger compass to do my navigating. I have traversed wilderness areas where I had never been before, and made it without any problem at all.
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In An East-West Degree, Increases |
