Simple, let say you have the following coordinates (a cross in concrete on the top of the hill in front of my parents' place):
Then call a USGS' web service from the URL below.
It says
getElevation
for Latitude 45.46 --> Y_Value=45.469678
for Longitude 10.97 --> X_Value=10.970527
return result in meters --> Elevation_Units=METERS
use the best survey available --> Source_Layer=-1
not other additional info --> Elevation_Only=true
http://gisdata.usgs.gov/xmlwebservices2/elevation_service.asmx/getElevation?Y_Value=45.469678&X_Value=10.970527&Elevation_Units=METERS&Source_Layer=-1&Elevation_Only=true
Why would you want elevations?
To plot an elevation chart of a bike or hiking tour.
Amazing what you can find around...
(This was inspired by http://econym.org.uk/gmap/altitude.htm)