JOSM/Plugins/measurement: Which distance between points is being measured?

Given a straight path drawn between points A and B with the measurement tool provided by JOSM/Plugins/measurement, which distance am I getting? Projected distance?

I’m measuring small paths, usually below 1km, but high slopes are frequent. I would like to avoid accumulation of measurement errors or, at least, be able to describe to others what are we actually measuring.


‘Think’ left bottom of status bar there’s the distance between last two nodes drawn or last node and current point not yet fixed. The measurement values pane shows the cumulative distance in a way between first and last node. If just 2 nodes, the left bottom status bar value and the measurement value distance agree, and they should, where in the screenshot it is 26.22 meters.

In the example of a bridge area, you get this with total circumference of 58 meters i.e 2x26.22 + 2x3

In editors like JOSM, it can be expected that distances are always projected (i.e. air line distance “as the crow flies”). Editors would normally not have any height information in the background to be able to take z-values/slopes into account. GIS also normally measure this distance unless you use special tools.

In this context, it would be interesting to know which distances are given by routers that work with digital elevation models in the background. As the differences between projected and “real” distances are usually small, I would also expect projected distances here.


I should have taken into account this answer to another question I asked recently.

I agree in general, although when planning/tracking mountain tracks with high slopes the difference could become relevant. I will do more research and keep this topic updated if I find any clues.

More insights will always be very welcome!

Not really. One of the steepest trails around here is the Manitou Incline [0]. It has an elevation gain of 615 meters in 1.4 km. That is over a 44% grade. It takes elite athletes about 30 minutes to do it (to go 1.4 km!) “Average” fit people take over an hour. If one takes the elevation into account, the distance is 1.529 km (sqrt(1400^2 + 615^2) - less than a 10% increase. In deciding whether this trail is suitable for someone, the grade would be much more of a factor than the 10% increase in length. Other trails will have a grade far lower, but then the increase in length becomes exceedingly small.

Great example of “relevant differences”! I’m myself involved in tracking/mapping some not-so-steeped trails in my area (Galicia, Northwest Spain). That is why I’m trying to get a more accurate idea about what we are actually measuring while planning with tools as JOSM. Thanks!