If you search in the Mathematica documentation for "DEM" you will see options for reading the data and metadata, which you will probably know how to interpret. In this example I am just using pixel count for the coordinates of the x and y axes, since I don't know how to convert to lat and long. Tooltip is used to display the elevation, when the cursor is put over a contour line. This is not quite what you want, but close.
file = "/Users/christopherpurcell/Desktop/dem_3009147ne.dem";
data = Import[file, "CoordinateSystemInformation"]
bounds =
Import[file,
"SpatialRange"] (* should be {lat, long} in dec degrees but must \
be something else, maybe meters *)
data = Import[file, "Data"];
size = Import[file, "Dimensions"] (* data array size *)
interp = ListInterpolation[Transpose[data]];
ContourPlot[
Tooltip[interp[x, y]], {x, 1, size[[2]]}, {y, 1, size[[1]]},
Contours -> Range[10], PlotPoints -> 50]
The next step might be to put a ReliefPlot of the data in a Manipulate, and return the elevation value that corresponds to the cursor location.
Something along these lines, where if you click on a point, you get a display of the elevation in meters. (I think).
Manipulate[
ReliefPlot[ data , FrameTicks -> True,
PlotLabel -> ToString[Join[x, {interp[Apply[Sequence, x]]}]],
ColorFunction -> "LightTerrain",
PlotLegends -> Automatic], {{x, {1, 1}}, Locator}]
Next you would figure out the lat and long and use DataRange option to get the axes scaled correctly.
