Saturday, August 7, 2010

GPS Maps 106: How To Read A Topo Map

[This post is part six in a multi-part series about understanding the GPS system and its coordinate grid.

Being (hopefully) pretty much the last post in this series about reading topo maps, what we are going to discuss today is really "rubber on the road" stuff and, in large part builds upon what we've already discussed as well as using a slightly different technique than we've ever used in the past.

This is where we actually hold that piece of crumpled, soiled, many-times-folded paper in our hands and try to find "where the blazes are we?" … No kidding — go get your topo map. It's better if you actually have something to look at. I'll wait.

Ok, I'm trusting that you've come back with your map. I've got mine, which is the Devil's Throat, Nevada 1:24,000 quad. I'll be explaining using my map but yours should be almost identical in layout.

Before we begin you need to know a couple of things. First, we won't be repeating any of the basic material already covered. So, if you already know this stuff these will be great "live" examples of finding petroglyphs on Gold Butte. If you don't, the posts are still where we left them and you can review all of the "backgrounders" which are listed below.

And secondly, this tutorial is basically contained in an actual Google Earth Map using the "Tour" capability. If you haven't seen one of these before it's basically a map which you download then open in Google Earth.

Once you have it downloaded, you open it in Google Earth, wait for it to finish initializing all the graphics and zoom to the starting point (which in this case takes nearly 20 seconds so be patient), THEN click on the "Tour" placemark. That's all there is to it.

For the next several minutes (about 15 or so) you will be regailed with an audio explanation of what information is available on a USGS Topo Quad Map, accompanied by graphics, and the map automatically zooming around pointing out all the features. Quite a site!

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However, thirdly, I unfortunately have to tell you that Google Earth has chosen to "dummy down" their "free version" so that only computers containing graphics cards with memories large enough to support fairly substantial "texture sizes" [4000x4000 or more] can actually display these Topo Maps legibly.
[To see if yours is large enough: open Google Earth, click "help" → "about Google Earth" and see if "max texture size" is greater than 4000x4000].

If you have a "legacy" model computer you can still download and run the tour, and the screen will zoom all around the smaller graphics, but the actual topo map won't be legible. If you have an actual map in your hands to follow along this won't be a limitation – it just won't look pretty.

NOT TO WORRY THOUGH… after myself and several others, I recruited to "troubleshoot" this problem, spent over 100 hours to discover that this "poorly documented" inadequacy didn't have a work-around I've begun writing a "hard copy" version. It should follow closely behind this post.

Here is the link to the tour map: How To Read A Topo Map.

Click on the link, select "copy" or "download" from the dialog box to make sure it saves to your desktop. Then double-click on the file to open it in Google Earth. After the chugging and whirring have stopped, click on the "tour" link which will begin the media tutorial. It's really fun to watch (even if I do say so myself) and I've been told is worth the download wait.

Previous GPS Maps Posts

Next, the "paper" version.


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