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Usgs Units


bhines
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I'm going to Alaska at the end of this month (to the Brooks Range)and I understand that the lodge is going to provide us with USGS maps of the area that we are going to. This is one of those trips where they drop you off by sea plane ( on a lake) and pick you up at a different location 9 days later. I've got a garmin 60CS and have not used the USGS maps before. Will I need to convert the units (ie degrees decimal minutes to something else), or use a totally different system (WGS84 vs another type)? I've not been able to secure a map to experiment with, so I want to get it straight in my mind before I go. Oh yes by the way I did read that article last week about the Alaskan campers getting eaten by a grizzly bear. Don't remind me.

 

Bruce Hines

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Alaska would have the same USGS topo mapping as the lower 48. If you have a hardcopy topo in hand they are in Lat/Lon NAD27 datum. There are grid ticks along the edges for Lat/Lon, UTM, MILS, and I'm sure Alaska State Plane. For your use (depending on what that is) UTM way be a grid to set your 60CS to if you are pulling coordinates off the topo. Otherwise stick with WGS84 and know there will be a shift. The shift is shown in the topo map legend I think in the lower left corner of your quad.

 

Here's a thought. Garmin MapSource US Topo covers Alaska at 1: 100,000 scale just like the lower 48 and Hawaii. It might be worth the ~$99 to be able to load up mapping into your 60CS and run with it. I would!

 

Good luck up in Alaska, wish I was going!

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No there is no guide, only a location to meet the plane 9 days later. My brother is coming along and has been doing this for 10 years so we should be OK. I do have the topography maps for alaska for my GPs but I need to correspond that map with the USGS maps which I now understand uses a different UTM datum. Any help is appreciated

 

Bruce Hines

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Give them a call and confirm what the datum of the particular maps is. You can change the datum of your 60cs to match the maps they will provide. Go to the 60CS set up menu, then to "units", then to "map datum", and you can see all your choices for different datum. You might be more interested in the coordintes of the "pick-up" point than anything else.

 

I don't quite see the necessity of having the GPS use the same datum as the maps. Regardless of what you have the GPS set to you will see on the topo map, a fairly accurate representation of where you are..EG 1/2 way down the south side of "lost mountain"...by looking at the Gps location on screen and the terrain in front of you, you should have no problem correlating the GPS position to the paper map without necessitating converting coordinates from one to the other. I think you might be reading more into this than necessary.

 

I used my own "homemade" maps I up-loaded to my 60CS in the Adirondacks this weekend and I had no problem using the GPS in WGS84 finding my location on a paper map (NAD 27), over and over again.

 

It was previously stated that all of the US USGS maps are NAD 27...this is not correct. Depending on the area, many maps still remain NAD 27 and some are NAD 83, and many are in the process of being converted to NAD 83. You must check your particular map version to be sure.

 

Steve

Edited by stevesisti
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