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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 do not have a direction.
The incline is most commonly given as percentage values (postfixed with a percent sign, %), e.g. incline=15%. Degree-values should only be used where they are common (postfixed with a degree sign, °), e.g. incline=10°.
Positive values indicate movement upward in the direction of the way and negative values indicate movement downwards in the direction of the way.
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.
Relationship between percent and degree values
A rise of 1 meter vertically for every 1 meter horizontally can be represented as 100% or as 45°. In the UK this may be signed as '1 in 1'.
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 %> = tan(<incline in °>) * 100
<incline in °> = arctan(<incline in %> / 100)
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 somewhat 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 results in too big values.
Maximum known inclines on public streets is 37% at Canton Avenue - the steepest officially recorded public street in the United States. 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 are around 100% (i.e., Piste de l'Aigle in Zinal, Switzerland, around 100%, or 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.