I understand that coordinate system mismatches between layers is a relatively common problem. Nevertheless, exploring other posts hasn't helped me understand my issue. In short, I have a DEM raster and a KML route, and they should overlap based on geography alone, but they do not.
I have downloaded a Vermont statewide DEM raster (the top option, "ALL_Elevation...") from this link: http://vcgi.vermont.gov/opendata. The data is in the NAD83 coordinate system per the included metadata text file.
I also have a KML file of a hike in Vermont in the WGS84 coordinate system. I'd post it here, but unfortunately, I cannot find a method of uploading the file with this post! It was generated using a GPS watch, and it happily imports into Google Earth without an issue. (I can send along the route if it may help troubleshoot this issue. Please just let me know.)
Attempts at a Solution
I've tried to first add the DEM file, set the project coordinate reference system (CRS) to NAD83 to match the DEM, enable "on the fly" CRS transformation, and then add the KML file. This did not work.
The opposite order didn't work either (i.e., first add the KML file, set the CRS to WGS84, enable "on the fly" CRS transformation, then add the DEM).
I've also attempted to add just the KML file to a new project and "reproject" the file using Save As and saving the file with a new name and using the NAD83 CRS. Adding the new and "reprojected" layer didn't overlap the DEM either.
Lastly, I've read in another post that data using a WGS84 CRS will have negative easting values. I would tack on the negative sign to all easting values just to try this, but I'm uncertain how to access the raw KML data.
I'm running OS X 10.11.4 with QGIS 2.4.0 Chugiak.
Although I still haven't figured out what is going wrongly here, I do think that the issue is related to QGIS being unable to identify all the pertinent CRS information from the DEM layer. I think that a solution may involve defining a custom CRS using the "right" Proj4 code that matches my DEM. Proj4 codes can be found here: http://www.spatialreference.org. I've tried a couple different custom CRS ideas, but nothing works yet...