|man_made = embankment|
|An artificial steep slope|
|Rendering in OSM Carto|
|Group: Man made|
|Used on these elements|
|Status: de facto|
|Tools for this tag|
man_made=embankment is used to map an artificial slope or steep incline built for example to provide a level platform on top for a road or railway line (See embankment) or to otherwise shape or stabilize the terrain. Such a structure can be built from compacted earth (often stabilized with grass or other plants) or from loose or set stones.
How to map
man_made=embankment should be added to a way drawn with the lower side on right side of the way's direction.
This tag may be used on open ways (open polylines) as well as closed ways (closed polylines). So when drawing a closed polyline:
- a clockwise line has the lower side on the inner side
- a counter-clockwise line has the lower side on the outer side.
It is often rendered with a line featuring dots, triangles or other shapes on the right side to indicate the direction of slope. This is similar to the technique used for barrier=retaining_wall and natural=cliff. However, as a feature in the real world an embankment will have a much more significant horizontal component (both on its slope and on its crest) than a cliff, since a cliff is (nearly) vertical.
Raised roads, railways, etc.
When mapping a raised highway, railway, waterway or similar with artificial slopes on both sides embankment=yes can be used to document this in a very compact form without additional geometries, although this gives less information about the geometry of the embankment and can be confusing when there are several ways on the same embankment. Therefore some mappers prefer to map the embankment as a separate element instead of (only) a tag on another element. To do that you map two separate ways on both side of the road or railway line in different directions (according to the rule above) and tag them man_made=embankment.
If the primary function of an artificially raised ridge is protection from flooding you should use man_made=dyke to indicate that.
Elements of an embankment
To avoid ambiguity when interpreting the tag described in this wiki, it is helpful to document how this wiki relates to the way embankments are described in regular sources.
For instance: the British Environment Agency gives the following diagram of an embankment:
Among the elements described along with this diagram are (from left to right):
- Landward toe: the area at the base of the landward face of a raised feature (embankment, wall, cliff etc.)
- Landward face: the vertical or inclined part of an asset that faces the land or away from a reservoir
- Crest: the highest point of an asset (e.g. embankment, abutment, beach)
- Exposed face: the face of an asset that faces a river, coast or reservoir
- Berm: The extent of horizontal ground between the watercourse or coast and a raised feature (embankment, wall, bank, gate etc.)
Note that the "artificial slope or steep incline" mentioned in this wiki corresponds to the face of an embankment as mentioned as an element of an embankment in the diagram above. The crest (which is typically is not a slope) is also considered to be a part of the embankment here.
Actual usage, ambiguity and controversy
When mapping and when using OSM data it is relevant to know that the descriptions in this wiki have changed over the years and are ambiguous. So mappers give different interpretations to the scope and tagging method of this tag (see also Talk).
Some of the ambiguities with man_made=embankment include:
- the word used in the OSM-value for man_made=embankment typically refers to the embankment as a whole (sloping parts and the crest), but the focus in the descriptions and images used focus on the sloping part ;
- the instructions in "How to map" refer to a line with a with a high side and a low side, without making explicit if this is (a) the toe at the base of the slope ("face") ; (b) the crest at the top of the slope or (c) both ;
- some mappers argue that the mapping instruction says that only the top of the slope should be mapped (at the crest), but when only mapping a closed polyline along the crest, the geometry of the man_made=embankment-element in OSM will only consist of a fraction of the actual embankment in the real world, since the sloping parts of the embankment are not included in the geometry. Excluding the largest area (the sloping faces) of the embankment from the geometry for man_made=embankment is contrary to the emphasis on the slopes in both the definition of and image examples in this wiki ;
- however a well defined tagging scheme for describing the different elements of an embankment and their relations is not yet available. For the area of the slopes the non-documented tag man_made=reinforced_slope is sometimes used (Taginfo) but this is not explicit in the direction of the slope
Changes over time
- For most of the history of this wiki (from its start in 2011 to mid 2018) this wiki contained passages describing usage around raised land (which mostly points to the toe of the embankment, since from there on the land is raised) that have been removed without a reference to a wider discussion or proposal:
* To represent a raised finger of land [...] : draw two ways bordering the raised land[...]
* To present a banked enclosure (such as an iron-age hill fort): draw two ways with the outer way travelling anticlockwise and the inner way clockwise. Additional ways can be used to present ditches, scarps, aprons and terraces in large sites [..]
- For most of the history of this wiki (from its start in 2011 to mid 2018) this wiki indicated that man_made=embankment :
can also be an artificial bank raised above the immediately-surrounding land to redirect or prevent flooding by a river, lake or sea. See also: Proposed_features/Dyke (sic).
However, the current phrase "If the primary function of an artificially raised ridge is protection from flooding you should use man_made=dyke" was also introduced without a reference to a wider discussion or approved proposal ("Dyke"-proposal is inactive) and is problematic because some embankments can have a dual purpose (verifiability) and since dykes are a subset of embankments a subtag specifying the type of embankment would be more appropriate then an alternative tag at the same level.
Natural features with similar scope
- natural=earth_bank - earth bank is an abrupt change in ground level which can be clearly distinguished from its surroundings
- natural=gully - small scale cut in relief created by water erosion
- embankment=* - used to indicate a raised road or other linear feature with embankments on both sides
- cutting=* - the opposite situation with slopes towards the feature in question
- natural=cliff - for vertical or near vertical drops of natural origin
- barrier=retaining_wall - for a artificial vertical or near vertical built wall with a function similar to man_made=embankment
- man_made=dyke - for an embankment (or levee) to redirect or prevent flooding by a river, lake or sea