The distance or elevation data not precisely
what you expect for this route?
Data from a GPS device can be rough, especially in
areas where the terrain (trees, canyons) interfere
with GPS signals. And routes drawn on our maps are
reliant on people marking trails from satellite
images -- the details of which can be hidden by trees.
Elevation can be tricky too.
Elevation data is stored on spaced topographical
lines, and determining the elevation of a point
requires computers to estimate based on how close the
point is to the topographical line.
We mitigate this by calculating distance in
3-D (think Pythagorean theorem) and using mathematical
techiniques to smooth the elevation data. We come
close, but no one can be perfect with imperfect data,
even in
2018.