Forum Index > Trail Talk > UTM vs Lat/Long: Probably a really dumb question!
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Navy salad
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PostSat Jun 22, 2019 1:27 pm 
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Anyone know why UTM coordinates are given with the East/West coordinate (ie the equivalent of Longitude) first and the North/South coordinate (the equivalent of Latitude) second, when traditional non-UTM point locations are just the reverse (ie, Latitude first, then Longitude)?

I like UTM, but this has tripped me more than once!
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Anne Elk
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PostSat Jun 22, 2019 3:17 pm 
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See UTM entry here: https://en.wikipedia.org/wiki/Universal_Transverse_Mercator_coordinate_system

It seems to have something to do with easier calculation methods and had especial utility for WW2 applications.   Agreed it's confusing.

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Bernardo
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PostSat Jun 22, 2019 9:05 pm 
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I think it's because the X variable is independent and the Y variable is dependent.  It's much more intuitive to go over then up when plotting a location using coordinates.  Makes calling in artillery much easier.  Just my hunch.
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Vertec
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PostThu Jul 04, 2019 6:31 pm 
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UTM is a "flattened" map projection which "divides" longitude into zones, so the zone with its E/W coordinate appears first.  This made filing paper maps easier.  UTM zones each span 6 degrees of longitude so the numeric range of E/W is potentially smaller.

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Brian Curtis
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PostThu Jul 04, 2019 6:40 pm 
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FWIW, I write a fair amount of code that uses lat/long and the order is typically longitude than latitude. It is because, as Bernardo said, x (horizontal) then y (vertical) is the standard for most calculations.

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InFlight
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PostFri Jul 05, 2019 8:02 am 
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All the USGS, National Geographic, and Green Trail primary map grid lines are in UTM.  They include DMS Tick Marks along each axis as well.    When using paper maps, UTM coordinates are simply easier.

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hbb
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PostTue Jul 09, 2019 2:19 pm 
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To locate a position in the UTM system, the first thing you need to know is which one of the 60 longitudinal zones the position is in. Absent that information, you are dead in the water. So, right from the get-go, you have to start with an east-west "coordinate." The whole system keys off of that, those longitudinal zones are the primary reference point. It doesn't make sense to start with a north-south reference, because that could be in any one of the 60 zones.

I guess the reason that the system starts with longitudinal zones (as opposed to latitude bands) is that you want to carve out the ends of the zones to minimize distortion, like UTM does (the system only covers 84*N to 80*S). If you started with a latitude-based zone, the carve out wouldn't be over the poles as it is in UTM, it would be in the middle of the Atlantic ocean or something along those lines. Separating out the poles is pretty easy, because you can set the zones so they don't "cut off" part of a continent, or end up in the middle of some important shipping route.
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Navy salad
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PostWed Jul 10, 2019 11:22 am 
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hbb wrote:
To locate a position in the UTM system, the first thing you need to know is which one of the 60 longitudinal zones the position is in. Absent that information, you are dead in the water. So, right from the get-go, you have to start with an east-west "coordinate." The whole system keys off of that, those longitudinal zones are the primary reference point. It doesn't make sense to start with a north-south reference, because that could be in any one of the 60 zones.

Ahh, that makes perfect sense! I also found the comments about how the established convention for mathematical charts in general is to identify the "X" coordinate along the horizontal axis first, then the "Y" coordinate along the vertical axis logical -- to the point where it seems the "latitude first, longitude second" system is the one that's backwards!

Thanks for the comments!
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Forum Index > Trail Talk > UTM vs Lat/Long: Probably a really dumb question!
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