Key:ele

From OpenStreetMap Wiki
(Redirected from Proposed features/Altitude)
Jump to navigation Jump to search
Public-images-osm logo.svg ele
Key-ele mapnik.png
Description
Elevation of a point above sea level, in metres. Show/edit corresponding data item.
Group: properties
Used on these elements
may be used on nodesmay be used on waysmay be used on areas (and multipolygon relations)should not be used on relations (except multipolygon relations)
Useful combination
Status: approvedPage for proposal

ele=* specifies elevation (height above sea level) of a point, in metres. This is mainly intended for mountain peaks but could also be used for elevation of airport runways and many other objects.

For OpenStreetMap, this value should be in metres above mean sea level as defined by the  EGM96 geoid model. This elevation is usually very close to the national "above sea level" systems with differences < 1m. This is not the height above the WGS84 ellipsoid (see  geoid how these differ), which is shown as raw elevation by some satellite navigation devices, and which can differ from geoid elevation by up to 100 m.

In case of buildings and other man_made=* structures that stand on the ground, tag the elevation of the surrounding ground, not of the structure itself (i.e. do not tag the elevation of the tip of a tower; instead, set ele=* to the elevation of the ground level, and add the height with the tag height=*).

Basics

Main article: Altitude

OSM currently records points with their latitude and longitude (x/y coordinates). Elevations are only recorded for features where they are significant, such as peaks or surveyed points. Where this is done, the elevation above geoid (EGM96) is stored in the ele=* key. OpenStreetMap does not try to be a general elevation database, so do not tag elevation of nodes with no other tags, as well as for objects whose elevation is not an information of general interest.

The elevation in a local datum can be tagged as ele:local=*, with elevation specified in metres. A proposed notation to store vertical datums other than the EGM96 is ele:xyz=*, where xyz is the map datum, and the value is specified in metres.

Sources for elevation values can be signs or values from literature. Such values should also be checked for plausibility since elevation signs and official mountain heights are known to be frequently inaccurate. Another source of elevation data are GPS traces, but elevation values from these are usually much less accurate than the horizontal position. You also need to make sure values are in the correct coordinate system, or converted as necessary in case of ellipsoid-based elevations.

Another source of elevation data are gridded elevation data sets. Those are often used in outdoor maps to render relief, like OpenCycleMap and Reit- und Wanderkarte, and elevation values can be determined from displaying these maps as a background layer in editors. Beware, however, that such data sets contain significant rounding errors, and discrepancies from accurate elevation values can easily be as much as 50 metres.

Elevation information with sub-metre accuracy is rarely verifiable, so the values should be specified in integer metres.

National reference systems

Elevations posted on official signs are usually relative to the national reference system of the respective country and have to be converted to WGS84/EGM96.

Country Standard Common name Heights Tide gauge Reference point Conversion
Australia Australian Height Datum Metres above mean sea level 32 distinct tidal references points on Australian coastline. Ausgeoid09 Conversion calculator online
Austria Meter über Adria (m ü. Adria)
(metres above Adriatic)
Normal-orthometric Trieste 1875 Hutbiegl
Belgium meter boven Oostende Peil (m O.P.)
(metres above Oostende tide gauge)
Orthometric Ostende Ostende
Czech Republic Bpv (Baltic Sea vertical datum) metrů nad mořem (m n.m.)
(metres above sea level)
Normal (Molodenskii's) Kronstadt Kronstadt, Russia
Estonia BK77 Normal Kronstadt Kronstadt [2]
Finland N43,N60,N2000 Orthometric Helsinki Helsinki [3]
France (mainland) NGF-IGN69 mètres au-dessus du niveau de la mer (m)
(metres above sea level)
Normal Marseille Marseille [4]
France (Corsica) NGF-IGN78 mètres au-dessus du niveau de la mer (m)
(metres above sea level)
Normal Ajaccio Ajaccio [5]
Germany[note 1] DHHN2016 Meter über Normalhöhennull  Normalhöhennull Normal Amsterdam  Wallenhorst
Former West Germany[note 1]

</ref>

DHHN12 Meter über Normalnull Normal-orthometric Amsterdam Hoppegarten (near Müncheberg)
Former East Germany[note 1] SNN76 Meter über Höhennull (m ü. HN) Normal Kronštadt Hoppegarten (near Müncheberg)
Hungary Tengerszint feletti magasság Normal Kronštadt Nadap
Ireland metres above sea level (m ASL / m a.s.l.) Orthometric Malin Head Malin Head
Italy metri sul livello del mare (m s.l.m.)
(metres above sea level)
Orthometric Genoa Genoa
Japan[note 2] Tōkyō-wan heikin kaimen (東京湾平均海面)
(Tokyo Peil, T.P.)
Orthometric Chiyoda, Tokyo Nihon suijin genten (日本水準原点), 24.3900m
Liechtenstein LN02 Meter über Meer (m ü. M.)
(metres above sea level)
Marseille Geneva
Luxemburg Orthometric Amsterdam Amsterdam
Netherlands meter boven/onder NAP (m NAP) (metres above/under NAP) Orthometric Amsterdam Amsterdam
Norway meter over havet (moh.)
(meters above sea level)
Normal-orthometric Tregde Tregde
Poland metry nad poziomem morza (m n.p.m.) Normal Kronštadt
Portugal Nível médio do mar adotado (NMA) Orthometric Cascais Datum Altimétrico Nacional de 1938 (Cascais)
Russia BS1977 высота (метры) над уровнем моря
(elevation/metres above sea level)
Normal Kronstadt Kronstadt The pseudo-geoid model EGM2008BALT is available for St. Petersburg / Kronstadt area [6]
Slovakia metrov nad morom (m n.m.)
(metres above sea level)
Normal Kronštadt
Slovenia Normal-orthometric Trieste 1900 Ruse
Spain metros sobre el nivel del mar (msnm)
(metres above sea level)
Orthometric Alicante Alicante
Sweden RH2000 Meter över havet (m ö.h.)
(metres above sea level)
Normal Amsterdam
Switzerland [note 3] LN02 [ dubious ] Meter über Meer (m ü. M.)
(meters above sea level)
Marseille Geneva Transformation and calculation services
Turkey Normal-orthometric Antalya Antalya
UK - Great Britain Ordnance Datum Newlyn metres above sea level (m ASL / m a.s.l.) Orthometric Newlyn, 1915 to 1921 Newlyn OSGM02, Coordinate transformer
UK - Northern Ireland Belfast Ordnance Datum metres above sea level (m ASL / m a.s.l.) Orthometric Clarendon Lock, Belfast, 1951 to 1956. Clarendon Lock, Belfast
Former Yugoslavia Nadmorska visina (m/nv, ~metres above Adriatic) Normal-orthometric Trieste 1875/1900
  1. 1.0 1.1 1.2 DHHN92 was adopted gradually after reunification. Even newer topographic maps may still use the former reference systems. Former East Germany used DHHN-12 on the territory of East Berlin, in rail contexts and for inland waterbodies. See Bundesamt für Kartographie und Geodäsie (BKG):[1].
  2. National authorities use this datum only for the four main islands of Hokkaidō, Honshū, Shikoku, Kyūshū and associated islands. For Sado, Oki, Tsushima, as well as for the Izu, Ogasawara and Ryūkyū islands, the mean sea level of a nearby coast or bay is used. For example, the reference point for Miyake-jima, which belongs to the Izu islands, is the mean sea level of Ako Bay on the western coast of the island.
  3. LN02 remains in force. For LHN95, which uses orthometric elevations, the reference altitude of Repère Pierre du Niton was kept. See https://www.swisstopo.admin.ch/en/national-height-network-lhn95

Example

The height of Breithorn in Switzerland is 4 164 metres. It could be mapped as:

natural=peak
name=Breithorn
ele=4164

The height of rail tracks in Tanggula railway station is 5 068 metres. It could be mapped as:

railway=station
name=唐古拉
name:bo=གདང་ལ་།
name:en=Tanggula
name:zh=唐古拉
ele=5068

Local units

It's been noted that some elevations are more conspicuous than others, and the requirement that key:ele be in metres is unhelpful for denotation on mountain peaks in non-metric areas. Since locals in the United States (and certainly elsewhere) think of things like mountain elevations strictly in feet, there seems to be no good way to address this with the current framework.

  • It's tempting to enter an elevation with a unit of measure ("3045 feet") but the tag must be in metres
  • Some software relies on this tag being numeric metres

There is likely no good solutions to this without using a separate tag for tagging height in local units. As of September 2021, ele:ft=* is used on over 2,300 features, while about 600 features are tagged with feet or inches in ele=*.

Features with variable elevation

Most terrain features have a constant elevation, meaning the ele tag is unambiguous. There are some exceptions, however, that can offer challenges when mapping elevation.

One example of this is a reservoir. When using the ele tag on a non-intermittent, ordinary lake, if usually refers to the elevation of the (close to constant) water level. Since reservoirs have water levels that change within certain bounds, it is unclear how one should interpret the ele tag when present on a reservoir, as it could be referring to the maximum water level, the minimum water level, or something in between. There is not yet an agreed upon scheme for making the meaning more clear, but some mappers use the following tags to add clarity to the situation:

  • ele:min to denote the minimum water level achievable by regulation. Usually corresponds to the lowest point in the transition between a reservoir and a drainage tunnel/pipe.
  • ele:max to denote the maximum water level achievable by regulation. Can correspond to the level of the spillway, or higher. Might need further refinement.
  • ele:natural to denote the water level before the dam was built.

Possible Tagging Mistakes

If you know places with this tag, verify if it could be tagged with another tag.
Automated edits are strongly discouraged unless you really know what you are doing!
If you know places with this tag, verify if it could be tagged with another tag.
Automated edits are strongly discouraged unless you really know what you are doing!

See also

References