GPS measurments

[MIKE]

I am trying to remember how many miles there are in a degree and how many feet in a minute and how many feet in a second. Does anyone know. Thank for your help.

[JasonMN]

I am pretty sure one degree of Latitude is equal to 60 nautical miles. That's about 69 statute miles (1.15 x nautical miles = statute miles). So one minute of Latitude equals one nautical mile and one second of latitude equals 1/60th of a mile, or about 100 feet.

[Denied]

Latitude lines (running e & w) are 1 nautical mile apart, north to south. Longitude line (running n & s) seperation changes depending on where you are on the earth. ON LAKE ERIE they are ~.75 nm apart east to west. So 41 40.00N to 41 45.00N would be five nm. 083 00.00W to 083 05.00W would be 3.75 nm.
Hope this helps, we should get lots of help on this one :)Corrections, additions or throw it out and start over are welcomed.

[MIKE]

Thanks guys.

[JasonMN]

So I guess latitude lines occur every "minute" then?

[Riceburner]

This discussion encourages another question--My LMS350A manual describes the position screen as reading in degrees/minutes/thousandths of a minute. (N45 15.622 and W95 03.247) Some others here, and my older Garmin read out to two decimal places after the minutes (N45 15.62 and W 95 03.24)--I think I remember that there was a choice on the Garmin unit that read out in something other than degrees/minutes/hundredths of a minute. Can someone shed some light on the units of measure comparison/applications/accuracy....THX

[Gary B]

One MINUTE of latitude equals approx one nautical mile. 60minutes (per degree) times 360 degrees equals 21,600miles(approx circumference of earth). Using Degrees, Minutes, and thousandths of a minute(3 digits to the right of the decimal) will "theoretically" yield accuracy of approx 6 feet. That is in a perfect world, and God knows we humans have not achieved that yet. Using Degrees, Minutes, and Seconds (to two digits) will yield accuracy of approximately 100 feet. One tenth of a second of latitude would then be approx 10 feet(if your GPS will read this way). Usually there is enough inaccuracy that it doesn't make a lot of difference, but I do prefer Degrees, Minutes, Thousandths. Whichever one you use, check every map you use, every coordinate you use, to see which measurement is being used. I have seen some maps that had both! What a confusing mess! By the way, if you are confusing "59 Seconds of latitude" with "59 hundredths of a minute of latitude", the difference can cause an inaccurate reading of about 2400 feet(or 4/10 of a mile). Sounds like trouble, doesn't it. GPS's are one of the greatest tools a boater can have. They just take a little getting familiar with. Good luck!

[MIKE]

OK, let me get this staight. If my seconds read .190, how far am I away from .191 seconds. If my seconds read .190, how far from .120 seconds am I.

[RANGER]

Interesting discussion!

From what I gathered from Gary B's statement:

.190 to .191 = 6 ft

.190 to .120 = 420 ft

Theoretically, of course! ;)

I prefer mine to read in the thousands-of-a-second also. But, then again, I'm "Anal" anyway!

[MIKE]

Thanks, thats what I thought.

[Riceburner]

A little more info, PLS......from above " Using Degrees, Minutes, and Seconds (to two digits) will yield accuracy of approximately 100 feet. One tenth of a second of latitude would then be approx 10 feet(if your GPS will read this way)" ....in this format of Deg/Min/Sec, my old Garmin gave me a reading of N45 14.79 and W094 53.99 for a spot. The next unit to the north would be N 45 14.80 Theoretically, how far further north of .79 is .80 spot?? I think it's the "seconds" term that confuses me...is .10, .01, or .001 one tenth of a second? Dealing with distance, are there 100 seconds in a minute? THX.

[Dave S]

For measuring distances East and West the distance between lines of Longitude (the North/South lines) vary from an maximum at the equator to zero distance at the north and south poles. I believe you need charts based on your given latitude to determine the East/ West distance between say W 80.190 and W80.191

[Stotch]

Just talked with the company's licensed surveyor and the following is from his books.

For Latitude (going in an " East or West " direction around the globe) use the following info:

1 minute of Latitude = 1 nautical mile.

69.00 miles in a degree

1.15 mile in a minute of latitude

0.019166666 mile in a second


For Longitude (going in a North or South direction) it is not that easy - due to the egg shape of the globe and the poles. It really depends on where you are situated (North or South) for the system to calculate the Longitudinal information.


Hope that helps.........Stotch



Tight Lines !
Bent Rods !
Sore Hands !

[Gary B]

You can go to the menu in your GPS or the legend on a map to see which is being used. Or sometimes you can tell by the readings given as in this case. You gave readings of N45 deg, 14.79, and W094 deg, 53.99. In this case You are reading Degrees and Minutes to the hundredth of a minute. Notice that the decimal is in the second group of numbers. This is the "minutes" group. The " .79 " and the " .99 " are the decimal equivalent of part of a whole minute. You may see one, two, or three digits to the right of the decimal point (N45deg, 14.799min). For latitude readings: 1 minute = 1 mile. ".1" is one tenth(or approx 600ft), ".01" is one hundredth(or approx 60 ft), ".001" is one thousandth(or approx 6ft). Remember that longitude readings will be accurate (1 minute = 1 mile) at the equator, but will be more inaccurate the farther you are north or south from the equator. Take a map of your part of the world and compare latitude and longitude to get a rough idea how far 1 minute of longitude is.

You will always have EXACTLY 60 seconds in one minute, never any more. If the reading is given in Degrees, Minutes, and Seconds, it will look more like one of these: N45deg, 14min, 59 sec, or N45deg, 14', 59", or n45 : 14: 59. Notice the punctuation marks. A period indicates a decimal equivalent. Colons, apostrophes, and quote marks indicate Degrees, minutes, and seconds. If the reading goes to the tenth of a second it will look more like this: N45deg, 14' , 59.8" . Notice the ".8" at the end. 1 minute = 1 mile, 10 seconds = 1000ft, 1 second = 100 ft, .1 second = 10 feet

The distance from n45deg, 14.79 to n45deg, 14.80 would be very close to 600ft. Remember that 1 minute of latitude equals 1 nautical mile(approx 6080ft), so, one tenth of a mile is approx 600 feet. Hope I haven't caused more confusion.

[Tom Moe, Ashland, WI]

I, too, was confused about degrees and seconds and minutes. Not anymore. I don't use them... because I can't remember any of it when I need it.

The ABSOLUTE BEST WAY TO MEASURE DISTANCE, other than miles, is using the " UTM " setting in your GPS menu. That stands for Universal Transverse Mercator. DO NOT PANIC, I REPEAT... DO NOT PANIC.

UTM measures distance in meters. Although, this may be of a bit more assistance to you on land, it can be helpful on water, too. Everyone knows a meter-stick is just a bit longer than a yard-stick. Everyone also knows that the metric system is easier to divide than other units of measure because it's based on 10's. Therefore, it's a piece of cake to divide and get to a half, quarter, eighth etc., without knowing what a degree is. It's also a piece of cake in using maps since the meter legend is also noted on many maps...nothing to remember.

On United States Geographic Survey maps UTM marks are the blue grid marks, and they run from west to east, but that's not important right now. (I don't know if they are on nautical maps.) There are 1000 meters between the blue marks. Fold your map and you can determine the halfway mark... or 500 meters. Fold again and you can get 250 meters.

CAUTION: This guess-timation is more appropriate for shorter distances and you would need to get more proficient if exact measurements were needed...especially in orienteering or getting through large land areas. YOU CAN NOT COMBINE METRIC AND OTHER UNITS OF MEASURE. Don't think that 500 meters is a half mile...it isn't.

The really cool thing is that you can enter waypoints and travel to nearly the exact mark. You will never be able to figure out degrees, minutes, etc. that closely. With UTM you can actually add and subtract distances very easily. Especially if you want to enter waypoints off a map and then hit the GO TO button later on land or water.

This system is really easy to learn and I strongly urge anyone using GPS at the amateur level to switch over to it. How much easier is it to guess-timate 100 meters to 100 yards. (I know, meters are a bit more.) It's much more accurate that you using a sexton and the stars in your sparkle-tub.

Remember, it's not that important to be able to translate a half kilometer to a half mile. It's way more important to be able to find where you are using a system you understand and that you can use to locate yourself. This system allows that to happen: Latitude and longitude don't.

Get a book on maps/orienteering or check out the Internet for UTM. I've used it for years now and I promise it's worth checking out. By the way, it's realy handy for deer season, too. Or, for marking saddles in elk country, etc.

Good luck!
Tom Moe
Ashland, Wisconsin