User can enter a flat pace that will be used to determine pace and time by considering factors affecting pace.
Consider hills, by estimating percent of pace depending on steepness/elevation for each point. See plotaroute.com for example.
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More advanced and more complicated, consider runnability of each section (type of highway, surface, smoothness, trail_visibility, mtb:scale etc, depending on what's available)
User can enter a flat pace that will be used to determine pace and time by considering factors affecting pace.