Elevation completely wrong

Another observation. When I disable elevation correction, the min/max elevation data for the run seems correct. However, the elevation graph does not change. I guess the elevation graph uses corrected elevation data by default, and is not affected by changing the elevation correction setting for the run.

When I step outside my house, GPS and every map source I've checked puts me at about 55-58m elevation. Garmin, with corrected elevation data, puts me at 170m.
To be fair I live at the foot of a small mountain, so if Garmin where to place their "corrected" elevation point about 500 meters from my house, 170m would be correct elevation.

For me it makes absolutely no difference (max/min) if I disable/enable.

When the vivoactive came out, Garmin Connect didn't have "elevation correction" enabled for it (It should have, since the va doesn't have a baro). A friend of mine went for a walk in the "wilderness" and was excited about how far she'd ascended during the walk. I asked her to turn on elevation correction and see what it says (I expected a change, and there was, but it was very minimal).

Which I found odd, as for me, I'd see a difference of 100's of feet. But I do my walking in a city. I'm guessing, but maybe "elevation correction" uses "known elevations" from where you are to correct the data. In a city, that's well known, due to things like the street data, etc. If you are a ways away from "known elevations" (such as walking in the widerness), GC can't correct it as much.

The only real way to get better elevation data is probably to change to something with a baro (the fenix3, 920, Epix, etc I believe).

Or the new, the vivoactive HR. Per the specs, it includes a "Barometric altimeter" (as well as a HW Compass!)
https://buy.garmin.com/en-US/US/wearabletech/wearables/vivoactive-hr/prod538374.html

(I have "Time and Tempe" updated to show the current barometer reading, and I included that as well as a compass in "Hike" on the va-hr, in hopes that the data is available! And on the va-hr, the elevation/ascent/descent shown in Hike should be much more accurate)

The elevation corrections that Garmin applies are based on GIS data which is supplied by different organizations depending on where you are. So it can vary depending on location and whose data Garmin is using, for some areas there are more than one source, it can be very different.

This is also why, with a device that doesn't have a barometer, you'll get a flat line if you cross a bridge as it's showing the level of the water instead of the height of the bridge. In that case if you turn off the correction you'll get an approximation of the bridge height that's based on the GPS elevation but you'll be surprised at how much it varies when running across a very smooth bridge.

Sorry, I don't know what each services preferred GIS source is so I wouldn't want to hazard a guess.

Just like most map/directions websites have various Aerial ('satelite') views and photos ....and in photos are seamed together. The topographical GIS data (USGS (various years), Landsat, Garmins own data) that is used and stitched/estimated/extrapolated... together is also going to be different between companies.

Used to do GIS for a couple years while in college - cool stuff.

Here's just a little background data from the USGS - http://education.usgs.gov/lessons/geospatialwebsites.html