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In reviewing an application which was submitted by a new measurer, I decided to check his elevations by using Topo USA 5.0 which I usually use to get my elevations. He had used USGS maps at

I was amazed to see the differences! I went to the site he used and came up with the same numbers he did. We are talking streets in the middle of town here so it is easy to make sure the points sampled were identical.

With Topo USA I got the following elevations:
S - 532
F - 537
H - 537
L - 432

With the USGS maps I got:
S - 492
F - 500
H - 500
L - 412 (different location)

I could understand some very slight variation but 40'!

Have others had this experience? If so, does anyone have any idea why this is happening and which source is more likely to be accurate?
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Curious how Goggle Earth fairs in comparison to Topo USA 5.0 and USGS maps?

If there is this kind of inconsistency, a recommendation might be made as reliable sources to use.

At the USATF Course Certification - Tools for Course Measurers page there are the following recommendations – does each source give reliable data?

Mapping Information
The National Map is an online interactive map of the United States from USGS billed as "The Nation's Topographic Map for the 21st Century." Get precise coordinates, including elevations, by just clicking a point (no need to interpret contours). Includes lots of satellite imagery so you can zoom in and see landmarks that you can almost touch with your bike. It tends to be slow, but it's totally web-based, so doesn't require installing software on your computer and can be used from any computer.
Google Earth is a sophisticated tool with high-resolution streaming imagery that lets you "fly from space to your neighborhood" and also allows determining distances and elevations. It's available in a basic free version as well as a $20 "Plus" version with more capabilities (e.g., GPS data import and better printing) and a $400 "Pro" version for professional and commercial uses. All versions require installing software on your computer, currently available only for Windows (2000 or XP) and requiring a fairly high-powered PC.
Google Maps isn't as sophisticated as Google Earth, but is totally web-based, includes some satellite imagery, and is easy to use (e.g., you can drag the map with your mouse). It does not, by itself, allow measuring distances or elevations, but there are third-party tools built on top of Google Maps that add such capabilities: America's Running Routes from USATF allows measuring route distances. Gmaps Pedometer does this and also provides elevation profiles.
Traditional USGS Topographic Maps (which require interpreting contour lines to find elevations) may be viewed for free online at TopoZone or at Microsoft's TerraServer-USA site. Hard copies of these maps may be purchased directly from USGS or from Map Express, or you may search for a map dealer in your area. Unfortunately, these maps are getting out of date; USGS officially completed their series of 7.5-minute quadrangles in 1992 and has now replaced them with the National Map project.
Gmaps Pedometer will give you an elevation profile of your race route as you trace the route's path.

Here's an example:

I believe it only reports the elevations on points along your route that you click.(It doesn't show how the elevation changes between points that you click.) So you have to click a lot of points to get a detailed plot. The other problem is that it doesn't always work. Right now, for example, it is having problems.

It doesn't look like the measure tool in Google Earth will do this. At least I can't find it.
The definitive source for elevations is USGS. Others use their data to provide their own programs, with varying success.

An interactive USGS source is:

USGS National Map Viewer

It's slow but sure.

Actual USGS maps can be obtained at:

USGS Terraserver

By downloading the maps, and using cut/paste, a topographical map of an entire course can be made.

These two sources are the only ones I've found that are operated or sponsored by USGS. I trust no others.
I also use the USGS topographic maps for elevation and road information for some locations. But if I’m interested in some place near home, I use the City of Huntsville interactive maps at: This site provides good road detail, shows buildings, homes, parking lots, schools etc. and also gives five foot contour intervals when you zoom in. It can overlay other features and has a measurement tool that is a good aid for course layouts. But like the USGS site, it is slow. I know this won’t help many of you, but perhaps your city or county has a similar map service.

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