Definition of length
Yeh, Sure... You might be able to figure this one out yourself. But for those having a week spot for topography and geodesy, we do take into account the curvature of the Earth.
Difficulty level (relative)
The Difficulty level is expressed as a value 1/10 (very easy) to 10/10 (very difficult). 1/10 indicates that for this variable there are 90% of the routes more difficult. 10/10 indicates that for this variable there are 90% of the routes more easy.