Below is a portion of an Ordnance Survey map of central London, at 1/25000, obtained from:
View the map in 1/25000 at the above site. Here is a section of the map with three elevations shown. They were taken from Google Earth, and are in feet.
Note the three elevations appearing in red. They were obtained using Google Earth. To the left of each red elevation is a figure which shows the elevation in meters, according to the Landranger 1/25000 map. There’s quite a discrepancy.
Mike Sandford and I have been kicking this around. He converted my readings to meters and said:
OS map * Google * so google sea level datum is lower by
16 meters * 29 meters * 13 meters
2 meters * 15 meters * 13 meters
4 meters * 16 meters * 12 meters
The Thames moves up and down with the tide, and the Embankment, which borders the Thames, is considered to be about 5 m above mean sea level.
These are the biggest differences I’ve seen between Google and a trustworthy map.
Check it out! Any thoughts?This message has been edited. Last edited by: Pete Riegel,
What really matters to runners, and USATF/RRTC, is the change in elevation, right? So the datum doesn't matter much.
I am relatively new to this forum, so I do not know who likes or doesn't like GMaps Pedometer. I find it the easiest way I know to obtain elevation profile data for certification applications.
I also appreciate its usefulness for confirming an understanding of a new course route with a client.
lyman - does Pedometer allow you to save a course, send a link to your client, and have them able to edit the course (or for you to edit it, if they don't want to?). Last I checked, it didn't have the save-and-edit capability, which makes for a cumbersome Marathon edit.
I have found MapMyRun.com to be the best tool for me, for the editing reasons, especially. I use it for every route confirmation before I go out and measure.
Duane, GMaps does allow you to save a course and the elevation profile, and send the link to a client. However, it does not provide an editing capacity. Few clients I work with have the ability to use either MapMyRun or GMaps, it seems.
The last time I tried MapMyRun, many months ago, I did not see an option to draw a manual route. So, if a route traverses a paved path that does not show up on the map or parking lot, I was not able to complete the route on MMR, while GMaps does a fine job.
I do have one client who recently sent me MMRs of 2 courses he hired me to measure. In both instances, my GMap of the same route produced a distinctly longer 5K course. This resulted in a significantly different start and finish in each instance. The courses as measured turned out to be almost exactly what GMaps showed them to be - which was quite different than the MMR editions. I can send you or post the links if you or anyone is interested so you can see the differences.
BTW, you have an excellent Web site.
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