Map Datum Used???

[Sam Marti]

I have been trying to find out what Map Datum Google uses on its maps online and on cell phone maps for years now.  Recently I again encountered

folks trying to match coordinates given to them in one datum used by the Bureau of Land Management by entering the coordinates in their cell phone where

the datum used by Google is not published.  They were over 150 yards off on each coordinate boundary between BLM land and private land and were

trying not to trespass while elk hunting.  Their new cell phones and the ones used by my friends do not let them change map datum to match hard copy

maps or for entering coordinate data published in a different datum.  Seems like a simple fix would be just to tell us what datum Google uses and to tell

their map users to make sure they match the datum as well as the coordinate system used.     ie.  WGS84 or NAD27Conus

[Andrew Sawyer]

Interesting question. I don't know, possibly in the Maps Product group would be the answer to your question.

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From: Sam Marti via General Map Maker <google-mapmaker+noreply-APn2wQf-...@googlegroups.com>

Sender: General Map Maker on behalf of Sam Marti <google-...@googlegroups.com>

Date: Wed, 31 Oct 2012 18:03:57 -0700 (PDT)

To: <google-...@googlegroups.com>

ReplyTo: General Map Maker on behalf of Sam Marti <google-...@googlegroups.com>

Subject: Map Datum Used???

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[Craig Hartel]

I use a custom Albers Conical projection at work. I even have some UTM NAD82 Z10 stuff as well. When I upload a KML to Google Maps or Google Earth, the features are reprojected on the fly. As long as your KML has the projection used included,  you need not know what Google is using.

[Saikrishna Arcot]

I think they are using multiple coordinate systems, but combining the data into one standard coordinate system (therefore, the possible differences when copying coordinates).

[trailman]

Google is using WGS84. Your friends probably entered coordinates in NAD27, which is on the old USGS / BLM topos.

[Craig Hartel]

The point is, as long as you use a real projection and as long as your KML includes the projection information, the data will be transformed on the fly. If your data doesn't include projection information, then you may as well have drawn it on a piece of paper with a crayon because no mapping system can deal with that.

In my job every day I deal with data from multiple projections - and since the data comes with projection info, I don't even have to think about the transformation because the GIS server does all the work for me.

[Sam Marti]

Trailman.  Thanks. Sam

On Thu, Nov 1, 2012 at 3:33 PM, Craig Hartel via General Map Maker <google-mapmaker+noreply-APn2wQdV...@googlegroups.com> wrote:

The point is, as long as you use a real projection and as long as your KML includes the projection information, the data will be transformed on the fly. If your data doesn't include projection information, then you may as well have drawn it on a piece of paper with a crayon because no mapping system can deal with that.

In my job every day I deal with data from multiple projections - and since the data comes with projection info, I don't even have to think about the transformation because the GIS server does all the work for me.

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[Sam Marti]

Craig Hartel - I agree, if you don't have the projection and especially if you are not literate on map making, you might as well

draw a crayon and paper map.  Thanks  your comment made me laugh.  Sam