For marking a way's incline (or steepness/slope). In the case of roads, there is often a warning sign along the road.
Split the way at the ends of the steep section and add a tag incline=value% on the way with values as given below. The value should be given for the practical maximum incline on the steep section (i.e., the maximum incline that a vehicle/primary user could achieve), and not for the average incline between the nodes. See Talk:Key:incline.
The use of this tag has limited (if any) usage, as nodes does not have a direction.
Percentage values are the default. A percentage value (postfixed with a percent sign, %) gives, when multiplied by the horizontal distance travelled, the corresponding vertical distance. That is, a value of 100% (for a street going uphill) would indicate a 45° angle, or, for 1 m horizontal travel, 1 m vertical gain.
Degree-values should be used where common and are postfixed with a degree sign, °; e.g., incline=10°.
Note that a 10° incline is not the same as a 10% incline. A 10° incline is actually a 17.63% incline, and a 10% incline is actually a 5.71° incline. Values can be converted as follows:
- <incline in %> = tangent(<incline in °>) × 100
- <incline in °> = arctangent(<incline in %>/100)
Positive values indicate movement upward in the direction of the way and negative values indicate movement downwards in the direction of the way (the way direction being the direction in OSM).
If the percentage of incline is unknown you can use incline=up or incline=down. These values refer to the way direction, too: up represents an unknown positive value, down an unknown negative value.
In case you don't know the exact value you can either
- Use incline=up for ways going up the hill, and incline=down for ways going down the hill or
- Roughly estimate and don't mind if it is completely wrong; it would be helpful to add another tag like FIXME=check incline
Common and extreme inclines
Common values for this tag are in the range −25% to 25% on roads. Ways with a steepness of under 10% are seldom signposted, except on motorways in mountainous regions, but inclines of over 20% are rare and pure visual estimation of steepness often leads to too big values.
Maximum known inclines on public streets is 37%. Standing upright in an incline of 52% (found in downhill pistes) can already be tricky, and not only because the shoes start to slip. The steepest groomed skipistes piste:downhill are around 100% (i.e., Piste de l'Aigle in Zinal Switzerland around 100%, Harakiri in Mayrhofen Austria at 85%). Offpiste skiing takes place on even steeper terrain for experts only.
One stated maximum incline for a way usable in a wheelchair has been 6%.
All kinds of highway tags, including steps.
highway=incline and highway=incline_steep.