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Calculate minutes/seconds on latitude/longitude

Mattatron

Now with extra pork!
pilot
#1
Please forgive me but I'm from Colorado and have no experience with reading maps larger than a state park. What I am looking for is a clear/concise gouge on how to calculate minutes and seconds with latitude and longitude. I understand the basics but have an old FM1-240 as a sole reference that is just confusing the hell out of me. Does anyone have a decent gouge or a "for dummies" manual on the subject? Any help would be greatly appreciated.

thanks,

Matt
 

HokiePilot

Well-Known Member
pilot
Contributor
#2
Everything before the period is the degrees. Take what is after and multiply by 60. What is before the period of is the minutes. Do the same thing again to get seconds.

Example 41.42876 degrees

41 degrees

.42876 *60 =25.7256

25 minutes

.7256*60=43.536

43.5 seconds

=41 degrees 25' 43.5"
 

Mattatron

Now with extra pork!
pilot
#3
Ok, that makes a lot of since. That being said, I am willing to run the risk of sounding dumb by asking if you could explain how to get the degrees in decimal notation? I understand that this is probably far more complex than I realize and the limit of my understanding stops at where the lat and long lines intersect on the globe. Really what I am looking for is where to go from there, or at least a point in the right direction. Again, any help would be fantastic.
 

HH-60H

Manager
pilot
Super Moderator
Contributor
#4
If you do the reverse of what HokiePilot demonstrated, divide by 60 rather than multiply, you get lat/long in decimal notation.
 

Mattatron

Now with extra pork!
pilot
#5
Ok, so from Hokies example of "41.42876 degrees". Where does the .42876 come from and if I were sitting in front of 1:250,000 scale map would I be able to accurately get seconds from a map of that scale, or would you just leave it at minutes? What I am really confused about is, with such a small area to measure, how do you get such an exact number with a ruler or plotter? Sorry for being persistent but this is something that has bugged me for a while I would really like to learn it.
 

HokiePilot

Well-Known Member
pilot
Contributor
#6
Well, first of all, if you were looking at a 1:250000 scale map, you would never get something that precise. Points on USGS maps are drawn to an accuracy of 1/50 of an inch. That would correspond to about 400 feet, about 4 seconds of latitude (more in longitude, it depends), or .001 degrees latitude.

To get more precision, you will need a larger scale. A normal USGS map, the 7.5 minute quadrangle has a 1:24000 scale. Practically, this gives you another decimal point of precision.

Go here to find out how to read it off a map http://www.map-reading.com/ch4-1.php
I know it is somewhat confusing, but that is the best that I could find in a quick search.

Or you can just look at your GPS
 

HH-60H

Manager
pilot
Super Moderator
Contributor
#7
Ok, so from Hokies example of "41.42876 degrees". Where does the .42876 come from and if I were sitting in front of 1:250,000 scale map would I be able to accurately get seconds from a map of that scale, or would you just leave it at minutes? What I am really confused about is, with such a small area to measure, how do you get such an exact number with a ruler or plotter? Sorry for being persistent but this is something that has bugged me for a while I would really like to learn it.
Oh, I see what you are saying now. As far as I know most maps use deg/min/sec, not degrees in decimals. Mostly computer systems use decimals because it is easier to do the math.
 

Mattatron

Now with extra pork!
pilot
#8
Thanks guys, every other person I asked told me to look at a GPS and not bother with the math...another tried to teach me triangulation using trig functions. I was trying to get seconds from a 1:250,000 scale and thought I was loosing my mind trying to figure out how yall could get such accurate notation from a tiny little plotter. Nice to know I was looking at the wrong maps. Thanks for the help fellas.