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WGS 84   Mathieu Cain Aug 15, 2009
Re: WGS 84   William Huber Aug 15, 2009
Re: WGS 84   Mathieu Cain Aug 17, 2009
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Subject WGS 84 
Author Mathieu Cain 
Date Aug 15, 2009 
Message Hello,

Could someone explain to me the naming convention for the WGS 84 geographic coordinate system? why is it that the projected UTM Zone maps show lettering from A-Z, while the projections themselves (e.g., in a ArcGIS) only appear as S or N? The A-Z convention makes sense to me, though the S or N, which I am assuming is simply referring to South and North, would mean the zones are massively "taller" strips. I am obviously missing a key point here.

Thanks for your thoughts. 
   
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Subject Re: WGS 84 
Author William Huber 
Date Aug 15, 2009 
Message You're not missing anything Mathieu, except you do seem to be confusing WGS 84 with UTM. The former is a datum--a description of the size and shape of the earth used for georeferencing--while the latter is a coordinate system based on the TM projection.

The full UTM system includes a series of 60 partially overlapping meriodional strips, each subdivided by ranges of latitude designated by letters A, B, ... (they don't go all the way to Z; they stop at X). The use of letter designations has its place, but not (usually) in a GIS. For GIS work one doesn't need to know the redundant letter code for latitude. Instead, all that's needed is to know the zone and whether it's in the northern (N) or southern (S) hemisphere. There definitely is opportunity for confusion because "N" and "S" now have two distinct meanings each, so you have to know the context in which any UTM coordinate is named.

The Wikipedia article on UTM provides details. See especially the paragraph headed "note of caution." http://en.wikipedia.org/wiki/Universal_Transverse_Mercator_coordinate_system 
  --Bill Huber
Quantitative Decisions (http://www.quantdec.com )
More GIS Q&A at http://gis.stackexchange.com/q/3083/664 
   
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Subject Re: WGS 84 
Author Mathieu Cain 
Date Aug 17, 2009 
Message WGS 84 is a geographic coordinate system is it not? while UTM is a set of projections of that geographic coordinate system (i.e., for flattening purposes)?

From my basic understanding, I suppose we shouldn't be labelling zones S and N but actually South and North to avoid confusion? if working with degrees (and not wanting to go negative), I could understand why one might want to specify a North angle vs. a South angle. I therefore agree entirely with that "note of caution" you pointed me to. Pity little has been done to remedy it.

Thanks for your comments.