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Metatags

Table of contents

  1. Metatags

Metatags are extra tags available, in order to display more data or to give better questions.

They are calculated automatically on every feature when the data arrives in the webbrowser. This document gives an overview of the available metatags.

Hint: when using metatags, add the query parameter debug=true to the URL. This will include a box in the popup for features which shows all the properties of the object

Metatags calculated by MapComplete

The following values are always calculated, by default, by MapComplete and are available automatically on all elements in every theme

_lat, _lon

The latitude and longitude of the point (or centerpoint in the case of a way/area)

_layer

The layer-id to which this feature belongs. Note that this might be return any applicable if passAllFeatures is defined.

_surface, _surface:ha

The surface area of the feature, in square meters and in hectare. Not set on points and ways

This is a lazy metatag and is only calculated when needed

_length, _length:km

The total length of a feature in meters (and in kilometers, rounded to one decimal for '_length:km'). For a surface, the length of the perimeter

Theme-defined keys

If 'units' is defined in the layoutConfig, then this metatagger will rewrite the specified keys to have the canonical form (e.g. 1meter will be rewritten to 1m; 1 will be rewritten to 1m as well)

_country

The country code of the property (with latlon2country)

_isOpen

If 'opening_hours' is present, it will add the current state of the feature (being 'yes' or 'no')

This is a lazy metatag and is only calculated when needed

_direction:numerical, _direction:leftright

_direction:numerical is a normalized, numerical direction based on 'camera:direction' or on 'direction'; it is only present if a valid direction is found (e.g. 38.5 or NE). _direction:leftright is either 'left' or 'right', which is left-looking on the map or 'right-looking' on the map

_direction:centerpoint

_direction:centerpoint is the direction of the linestring (in degrees) if one were standing at the projected centerpoint.

This is a lazy metatag and is only calculated when needed

_now:date, _now:datetime, _loaded:date, _loaded:_datetime

Adds the time that the data got loaded - pretty much the time of downloading from overpass. The format is YYYY-MM-DD hh:mm, aka 'sortable' aka ISO-8601-but-not-entirely

_last_edit:contributor, _last_edit:contributor:uid, _last_edit:changeset, _last_edit:timestamp, _version_number, _backend

Information about the last edit of this object.

sidewalk:left, sidewalk:right, generic_key:left:property, generic_key:right:property

Rewrites tags from 'generic_key:both:property' as 'generic_key:left:property' and 'generic_key:right:property' (and similar for sidewalk tagging). Note that this rewritten tags will be reuploaded on a change. To prevent to much unrelated retagging, this is only enabled if the layer has at least some lineRenderings with offset defined

_geometry:type

Adds the geometry type as property. This is identical to the GoeJson geometry type and is one of Point,LineString, Polygon and exceptionally MultiPolygon or MultiLineString

_level

Extract the 'level'-tag into a normalized, ';'-separated value

Calculating tags with Javascript

In some cases, it is useful to have some tags calculated based on other properties. Some useful tags are available by default (e.g. lat, lon, _country), as detailed above.

It is also possible to calculate your own tags - but this requires some javascript knowledge.

Before proceeding, some warnings:

  • DO NOT DO THIS AS BEGINNER
  • Only do this if all other techniques fail This should not be done to create a rendering effect, only to calculate a specific value
  • THIS MIGHT BE DISABLED WITHOUT ANY NOTICE ON UNOFFICIAL THEMES As unofficial themes might be loaded from the internet, this is the equivalent of injecting arbitrary code into the client. It'll be disabled if abuse occurs.

To enable this feature, add a field calculatedTags in the layer object, e.g.:


"calculatedTags": [

    "_someKey=javascript-expression",

    "name=feat.properties.name ?? feat.properties.ref ?? feat.properties.operator",

    "_distanceCloserThen3Km=feat.distanceTo( some_lon, some_lat) < 3 ? 'yes' : 'no'" 

  ]

The above code will be executed for every feature in the layer. The feature is accessible as feat and is an amended geojson object:

  • area contains the surface area (in square meters) of the object
  • lat and lon contain the latitude and longitude

Some advanced functions are available on feat as well:

distanceTo

Calculates the distance between the feature and a specified point in meter. The input should either be a pair of coordinates, a geojson feature or the ID of an object

  1. feature OR featureID OR longitude
  2. undefined OR latitude

overlapWith

Gives a list of features from the specified layer which this feature (partly) overlaps with. A point which is embedded in the feature is detected as well. If the current feature is a point, all features that this point is embeded in are given.

The returned value is { feat: GeoJSONFeature, overlap: number}[] where overlap is the overlapping surface are (in m²) for areas, the overlapping length (in meter) if the current feature is a line or undefined if the current feature is a point. The resulting list is sorted in descending order by overlap. The feature with the most overlap will thus be the first in the list.

For example to get all objects which overlap or embed from a layer, use _contained_climbing_routes_properties=feat.overlapWith('climbing_route')

Also see enclosingFeatures which can be used to get all objects which fully contain this feature

  1. ...layerIds - one or more layer ids of the layer from which every feature is checked for overlap)

enclosingFeatures

Gives a list of all features in the specified layers which fully contain this object. Returned features will always be (multi)polygons. (LineStrings and Points from the other layers are ignored)

The result is a list of features: {feat: Polygon}[] This function will never return the feature itself.

  1. ...layerIds - one or more layer ids of the layer from which every feature is checked for overlap)

intersectionsWith

Gives the intersection points with selected features. Only works with (Multi)Polygons and LineStrings.

Returns a {feat: GeoJson, intersections: [number,number][]} where feat is the full, original feature. This list is in random order.

If the current feature is a point, this function will return an empty list. Points from other layers are ignored - even if the points are parts of the current linestring.

  1. ...layerIds - one or more layer ids of the layer from which every feature is checked for intersection)

closest

Given either a list of geojson features or a single layer name, gives the single object which is nearest to the feature. In the case of ways/polygons, only the centerpoint is considered. Returns a single geojson feature or undefined if nothing is found (or not yet loaded)

  1. list of features or a layer name or '*' to get all features

closestn

Given either a list of geojson features or a single layer name, gives the n closest objects which are nearest to the feature (excluding the feature itself). In the case of ways/polygons, only the centerpoint is considered. Returns a list of {feat: geojson, distance:number} the empty list if nothing is found (or not yet loaded)

If a 'unique tag key' is given, the tag with this key will only appear once (e.g. if 'name' is given, all features will have a different name)

  1. list of features or layer name or '*' to get all features
  2. amount of features
  3. unique tag key (optional)
  4. maxDistanceInMeters (optional)

memberships

Gives a list of {role: string, relation: Relation}-objects, containing all the relations that this feature is part of.

For example: _part_of_walking_routes=feat.memberships().map(r => r.relation.tags.name).join(';')

get

Gets the property of the feature, parses it (as JSON) and returns it. Might return 'undefined' if not defined, null, ...

  1. key

This document is autogenerated from Logic/SimpleMetaTagger.ts, Logic/ExtraFunctions.ts