[Cdt-l] UTM vs Degrees

Brett blisterfree at yahoo.com
Sun Apr 14 00:25:18 CDT 2013

Hi Sage-

I think most hikers use and prefer Degrees and so forth because it's more intuitive than UTM. Latitude and longitude are sort of internalized during our school years as the natural way of thinking about geography and cartography. We learn that the equator is at zero degrees latitude, that the tropics of Cancer and Capricorn are at 23 degrees north and south latitude respectively, and that Prime Meridian (zero degrees) runs through Greenwich England, with "everything to the west" described as having "west longitude" and everything to the east having east longitude. Over time, and especially when we hikers spend many hours poring over maps, we gain an intuitive sense of what it means to say that the southern terminus of the CDT is around 32 degrees north latitude, or that the distance from one degree of latitude to the next is about 70 miles (on a south-to-north long-distance trail we might cover one degree of latitude each week, depending on the trail's
 exact layout). 

Of the three common formats for expressing lat/lon coordinates, probably the easiest format to grasp and utilize is Degrees and Decimal Minutes: DD MM.mmm. The degrees (north latitude in our case) would be anything between 0 (equator) and 90 (north pole), and for longitude (west longitude in the western hemisphere) 0 and 180. Decimal minutes simply represents the fraction of the degree, and works like the minute hand on the clock, running from 0 to 60, such that 32 and a half degrees would be expressed as 32 30.000. In this case, the decimal portion of the minutes is what would otherwise be expressed as "seconds," but seconds aren't really on a scale that we can easily visualize so are reduced to a standard decimal where they won't get in the way too much, but still contribute very nicely to the accuracy of the coordinate.

This may seem unnatural to someone who learned to use GPS in conjunction with UTM, but suffice it to say lat/lon has a lot of advantages and few disadvantages: Relatively easy to learn and use, widely employed on maps and in guidebooks, and plenty accurate for recreational use where UTM's touted extra precision is all but lost due to the lower resolution of standard topo maps and handheld GPS units (as compared to more scientific pursuits).

As for how to make "the switch" - there's a setting for that in your GPS unit's menus. Changing UTM to DD MM.mmm will allow you to hand-enter coordinates in the new format and will give waypoint and current position info in Degrees / Decimal Minutes.

Good luck!

- blisterfree

> Howdy folks!
     I just wanted to throw out a big thanks to all of you GPS Geeks (I mean that in the most endearing way possible) for finally explaining why a datum setting in my GPS might matter. I never hike with a GPS (I will be this summer on the Oregon Desert Trail though..), but I take data on my unit everyday as a tortoise biologist. I always wondered what the consequence was if I was using a different datum than someone else, now I know! 100' is a big deal when I'm collecting data!
      Another GPS issue I have been encountering lately is that my gps is consistently about 5 meters off of my co-worker's. We are both using the same datum (NAD83). We have changed batteries, turned them off and on, I even cursed mine and then ignored it (it sometimes works, I swear!) Any thoughts on how to "re-calibrate" a GPS? Might it be broken?
     Another question I have is about UTM's vs Lat/Long. As a biologist I have always used UTM's, but the current project I am on is using Lat/Long. Maybe it's just because I don't like dealing with all the extra digits of lat/long, but I haven't warmed up to using them. Do any of you use lat/long? Why? Does anyone have any tips for a simple way to make the switch from my UTM focused universe to a jumble of degrees, minutes, seconds, and decimal places?
       Thanks, and I hope the wind storms that keep spitting dust in my eyes here in the Mojave aren't slamming those NOBO hikers right now. If they are I highly recommend getting some ski goggles!!!
         Happy trails!

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