Elevation profilesThe elevation profiles are made with elevation data from the ASTER global digital elevation model (GDEM) version 2, the "ele" tag in OpenStreetMap is not taken into account, nor are tunnels and bridges. ASTER GDEM is a product of METI and NASA.
If the route has more than two end points or consists of more than one segment, no profile will be rendered. The direction of the profile follows the route west-east or north-south. If routes had elements with roles such as "start" and "goal", and/or were listed continuously from start to goal, we might be able determine direction from the route relation itself. You might want to bear those things in mind if mapping routes on OpenStreetMap.
There are holes, so called "voids" for which we have no elevation data, these are visualized with holes in the elevation profile line.
Beware that while ASTER version 2 is probably the best free global DEM, it does have its limitations both when it comes to accuracy and coverage, see their validation summary report for more information. The inaccuracies are further exacerbated by the inaccuracy of the OSM data, a smoothing technique that we apply, and the resolution of the profile which becomes lower the longer the route is.