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CrunchyBill

USGS and Google Maps/Earth Inconsistencies

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In the course of attempting to double-check a puzzle I'm trying to create, I discovered that Google Earth and the National Map/USGS website seemed to offer inconsistent information about the waypoints I was researching.  Further checking confirmed numerous irreconcilable differences between information from the government site, on the one hand, and Google's information.

 

If I had tons of extra time, I would submit inquiries to USGS and Google.  As it is, I have already imperiled my day job by spending time on GC when I should be billing a client.  So, I'm posting this topic to crowdsource a solution.  Or at the very least confirm that I'm not simply boradcasting some sort of Harry-Dresden-like jinx when it comes to website interfaces.  

 

 

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Which USGS website?  There are a number of different databases out there.  Are you doing a manual query or using a REST interface?

 

Tell us the inconsistencies and maybe we can give a better answer.  Are they placenames, elevations, road locations, or what?

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Who to trust hmm? Just know this at one time Google miss identified a farm in South Dakota as MT Rushmore.

It was not fixed for a long time till it was pointed out in the news. I would check multiple resources for any info.

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Elevations.

 

I selected points using the Spot Elevation tool on the National Map viewer at https://viewer.nationalmap.gov/advanced-viewer/

 

I recorded the decimal lat/long coordinates withOUT truncating.  [Typo edited/corrected: I DIDN'T cut off digits.  D'oh. - Bill] To double check, I accessed Google Earth and entered the coordinates.  For each point I had (somewhat laboriously) selected, Google Earth returned different elevations than the USGS site.  GoogleMap ("Terrain" map enabled) also provides elevations.  The data from Google Maps were consistent with Google Earth's data . . . and inconsistent with USGS.

 

Arggggggh.

Edited by CrunchyBill

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1 hour ago, CrunchyBill said:

Elevations.

 

I selected points using the Spot Elevation tool on the National Map viewer at https://viewer.nationalmap.gov/advanced-viewer/

 

I recorded the decimal lat/long coordinates with truncating.  To double check, I accessed Google Earth and entered the coordinates.  For each point I had (somewhat laboriously) selected, Google Earth returned different elevations than the USGS site.  GoogleMap ("Terrain" map enabled) also provides elevations.  The data from Google Maps were consistent with Google Earth's data . . . and inconsistent with USGS.

 

Arggggggh.

 

Elevation is a trickier thing than you would think.  It is impossible to store the elevations for the entire world, and those elevations have to be corrected for the geoid, etc,  so various datasets have been generated. 

 

Google does not reveal their exact methodology, so I tend not to trust them.

 

The elevations I consider best are the USGS 1 meter data, but those don't cover that much area (although they have been getting better).  The data is best near population centers.  This data is generated from laser point cloud measurements.  Data only exist for the US.

 

Next in quality are the ASTER and SRTM datasets, which are built from radar interferometry from orbiting satellites (or, in the case of SRTM, the Space Shuttle).  Both claim 10 meter spatial resolution, but the elevation models are a little better because of the use of interpolating polynomials.  Both cover most of the land mass of the Earth.

 

But you need to realize that none of these data sets does particularly well in regions where the elevation is changing rapidly (like peaks for canyon walls) and they also do not do all that well in areas where hydrology can change the elevation significantly over relatively short time scales (like the California Central Valley).  If your puzzle relies on elevations in such a region, you might be out of luck.  If your puzzle does not take the geoid into account, it might be wrong even if the elevations were correct. I have one puzzle that relies on elevations in 2 places to be relatively good, but the effect of the geoid dominates there! 

Edited by fizzymagic
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2 hours ago, CrunchyBill said:

I recorded the decimal lat/long coordinates with truncating.  To double check, I accessed Google Earth and entered the coordinates.  For each point I had (somewhat laboriously) selected, Google Earth returned different elevations than the USGS site.  GoogleMap ("Terrain" map enabled) also provides elevations.  The data from Google Maps were consistent with Google Earth's data . . . and inconsistent with USGS.

 

I don't know about other places, but here Google Earth's elevations rely on samples that are too widely spaced to be useful. The landforms here are essentially an ancient plateau that was eroded by rivers and creeks then flooded by the rising seas at the end of the last ice age, so it's typically fairly flat land on top dropping off steeply into gullies, often with cliffs. Here's an example at the northern end of Pearl Beach just below the cliffs on the headland, where GE reckons the sea is 20 metres above sea level.

 

SeaAboveSeaLevel.jpg.732c2c729d8cc5cc9e83bd8805de5a1a.jpg

 

Edited by barefootjeff
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Thanks for the (incredibly quick) advice and assistance.  I'm going to figure out how to steer folks away from Google Earth and Maps . . . and now all I have to worry about is the local Admin Reveiwer.

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The "3D Buildings" function in GoogleEarth  affects the elevation.  (In Pittsburgh, it throws the elevation off by 4 to 6 feet.)

 

Joe

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