Re: RE: Surveyors: DMS vs UTM -- comments, please...

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Posted by Guy on May 09, 2002 at 11:56:37:

In Reply to: RE: Surveyors: DMS vs UTM -- comments, please... posted by Last Chance Rand on May 02, 2002 at 14:47:43:

True enough. in many GIS projects, UTM is used. In general, the difference shows up based on the area of the project. You should use DMS if your project is large, and UTM if you are looking at a small area.
The UTM system is a grid overlay of the DMS, and since it is a flat grid, it doesn't perfectly fit the spherical DMS system. since there are many grids, the error is not great, but still. if you are working on a project that has to include distances between two states, for instance, i would use DMS. UTM is better suited for all smaller projects, and since most projects don't need to figure distances over a large area, UTM is used.
Of course, the obvisous advantage with UTM is that the units are meters, which is about a yard. distances in DMS are hard to figure without some help. Especially on a small site. Do you know how far a Second is? north to south? how about east to west? and yep, they are not the same each way. UTM is.

one point that most people overlook with coordinates, is that the USGS 7.5" topo maps are only accurate to the width of their thinnest line. this is not more than 10 feet, but is probably 10 meters. i don't recall at the moment.


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