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confused about coordinates


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I posted a little time ago, but now that I have actually purchased a GPS, I am still confused. The GPS I have is a SporTrack Map. It of course shows lat and long, as well as other coordinate systems, like UTM. I am used to using the eastings and northings grid system on a topographic map. The map I am using uses this grid reference system. Only at the bottom right does it show the lat and long (35o 15', 138o 45') as well as a few other minor spots in the map margins. I know I can choose the map datum to use (I have chosen WGS84, as listed on the map). When I choose the UTM system, my position is shown as 54 313529E and 6139223N. Why the odd number of figures? Is this the actual map reference? I still don't know how to show the grid reference system on the map. I will be disapointed if I can't get the thing to show me the grid ref from the map so I can plot my position on the type of maps I use!!!!

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The UTM grid should be shown as a series of small grid marks on the perimeter of the map. The boiler plate text on the bottom of the map contains much helpful information. Unfortunately, much of it is technical terms.


The UTM coordinates are in meters, referencing from a starting point for each zone. The grid marks are commonly 1000 meters apart (or one kilometer, if you prefer) and the last three digits for each grid mark (000) are omitted.


Many people like to use UTM because the distances are constant in both directions, all three directions 1f you use elevation in meters. Makes field math much easier.


A number of sources sell plastic overlays with UTM ticks.



"The time has come" the Walrus said "to speak of many things; of shoes and ships and sealing wax, of cabbages and Kings".

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Hi Dave, thanks for replying. I have since found that the system I'm used to is MGRS (Military Grid Reference System--- I think). I have worked out how to get the GPS to use this system for the map I am using at the time (after choosing MGRS under coord system it asks for metres (scale?), I've entered 100 metres. Then it asks for Grid Type MGRS-1, MGRS-2, MGRS-3, I plucked MGRS-2. When I now save a waypoint, I enter what apparantly is known as the Grid Zone Destination which is listed on the map (e.g. 54HUG). This must identify the actual map. Then the Eastings and Northings reference (e.g. 135 392). So the ref becomes



135 392


to my place in Mt Torrens, South Australia.


This seems to be what I need.


I am still not sure about the "metres" bit. My map is a 1:50 000, and each grid square equals 1 Km square, 1000 metres x 1000 metres. But if I choose 1000 for this option I get a Grid reference (GR) of 14 39. I would expect a six figure reference. Also I'm not sure what MGRS is, But I WILL find out.


Another v long reply on this msg board, but it IS addicting, I always liked the technical part of navigating, and now it's even cooler with a GPS!


`When we were little,' the Mock Turtle went on at last, more calmly, though still sobbing a little now and then, `we went to school in the sea. The master was an old Turtle--we used to call him Tortoise--'

`Why did you call him Tortoise, if he wasn't one?' Alice asked.

`We called him Tortoise because he taught us,' said the Mock Turtle angrily: `really you are very dull!'

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