How to use it
- Set a start and an end for a straight line, or press Draw a line and click the corners of a path.
- Wait for the heights to load. The chart and the figures appear.
- Move over the chart for the height at any point; the dot on the map follows.
5 practical uses
- Preview the climbs of a walk, a run or a bike ride.
- Check a road or a rail line for gradients.
- Plan a water pipe, a cable or a drainage line.
- Check the line of sight between two points over hills.
- Compare two routes by their climb.
The maths behind it
The line is sampled at up to 200 points spaced evenly by great-circle distance, found by walking along the line. Each sample's height comes from the elevation model. Heights are smoothed with a three-point average; the climb is the sum of the positive differences, the descent of the negative; the grade of a step is the height difference divided by the horizontal distance.
Reading it
The climb adds up every rise along the line and the descent every fall, after a little smoothing, so a rolling road counts all its hills. The steepest grade is over one sample step, so it depends on the line's length: a 1 km line is sampled every 5 m, a 100 km line every 500 m, which flattens short steep bits. The straight line between two places ignores roads; for a route's profile, draw along it or load a GPX in the GPX viewer.
Heights come from the routing engine's elevation service (Valhalla at FOSSGIS, on SRTM and similar 30 m and 90 m models) and, if that is busy, from Open-Meteo's copy of the Copernicus 90 m model. They are the height of the ground in a cell of that size, so a point on a cliff edge or a narrow ridge can read some metres off, and buildings and trees are not included. Sea is 0.