We have in Switzerland a precise relief map, where roads and trails are sometimes well visible.
I know it’s against the policy to add trails based on some external sources like Google maps.
However, is it allowed to add a trail using a relief map or an aerial map?
I’m wondering if the only way to map is by doing the trail by myself.
Here one example of a relief map:
Additional information: the relief map is available on the OSM editor.
My understanding from this post is that we are allowed to use all the layers provided by OSM to add a trail, even if I didn’t record it with a trace:
Therefore to answer my own question, I would say: it’s allowed as long as the layer us available on the OSM editor.
I hope it’s correct 
Yes, and no. You can of course use SwissAlti3D relief map to draw paths, I even use it to re-align some. Under trees, this is sometimes the most accurate data available.
But no, you should not do it without being there: it’s amazing the number of historic path that can be seen this way but that have completely disappeared in reality (most often overgrown).
Thanks for the clarification.
That sounds good, indeed I’m only mapping when I’ve been there and hiked on the trail.
By the way, I’m wondering why not more people are using SwissAlti3d to align the tracks, since it’s very precise.
Because there is a lot of them 
swissAlti3d currently has limited coverage in high resolution and there are areas that do not have alternatives either (for example the LIDAR data for the canton of Zürich). But lots of people totally use DTMs to align tracks etc.
PS: this should have likely been posted in the Swiss category.
My apologies for posting in the wrong category, I’ve added now the flag for Switzerland to reduce ambiguity.
No apology needed
The Switzerland category is rather new, I’ve now moved your topic here (as a moderator of the category).
I sometimes use the combination of SwissAlti3D overlaid with the Strava Heatmap (in JOSM) to align already mapped tracks and/or add new ones that are used and avoid adding impassable tracks.
In unseren Wäldern gibt es viele Strukturen, die wie Wege aussehen, aber keine sind. Ich benutze das Relief häufig, aber nur zum validieren des bekannten Weges
I do not agree with the statement that you must have visited a place before mapping. It is important to be aware that paths might be visible on a relief map but not used anymore. However, the added value of being able to map paths/streams precisely in wooded areas outweighs the issue of mapping something that isn’t there anymore. Forest paths or forestry roads can be overgrown rapidly if they are not used anymore. If you visit a place, it might change in the following years. In my opinion, it is better to map as accurately as it is possible and best judgement. If somebody visits the place the appropriate lifecycle tags can be added.
Legacy maps are full with old, unmaintained, disappeared path that are of no use to anybody anymore.
We dont need to add any path, but we d like to map useful ones.
In Switzerland, high-resolution relief data is available (0.5 m resolution). In most cases, it is not that hard to identify paths that are in use. Of course, best judgment should be applied. To say that you only should use relief data if you visit a place goes in my opinion too far. You could apply the same logic to satellite imagery.
Whether a path is useful or not is highly dependent on a person. E.g. look at the following path (not mapped using a relief) [1] and compare it to photos of it [2].
[1] Way: 405474518 | OpenStreetMap
[2] Wasserflue, Ostgrat [hikr.org]
Sure, you can have other clues that the path is passing through tree cover.However I’ve seen a few nice tracks stopping at overgrown forestry tracks lately.
For mushrooms picking, having SwissAlti3d alone is just fine as it is
