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Metatags
Metatags are extra tags available, in order to display more data or to give better questions.
The 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](URL_Parameters.md) `debug=true` to the URL. This will include a box in the popup for features which shows all the properties of the object
_lat, _lon
The latitude and longitude of the point (or centerpoint in the case of a way/area)
_surface, _surface:ha
The surface area of the feature, in square meters and in hectare. Not set on points and ways
_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
_country
The country code of the property (with latlon2country)
_isOpen, _isOpen:description
If 'opening_hours' is present, it will add the current state of the feature (being 'yes' or 'no')
_width:needed, _width:needed:no_pedestrians, _width:difference
Legacy for a specific project calculating the needed width for safe traffic on a road. Only activated if 'width:carriageway' is present
_direction:simplified, _direction:leftright
_direction:simplified turns 'camera:direction' and 'direction' into either 0, 45, 90, 135, 180, 225, 270 or 315, whichever is closest. _direction:leftright is either 'left' or 'right', which is left-looking on the map or 'right-looking' on the map
_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
Information about the last edit of this object.
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.
In the layer object, add a field calculatedTags, 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
- overlapWith
- closest
- memberships
distanceTo
Calculates the distance between the feature and a specified point
- longitude
- latitude
overlapWith
Gives a list of features from the specified layer which this feature overlaps with, the amount of overlap in m². The returned value is { feat: GeoJSONFeature, overlap: number}
- ...layerIds - one or more layer ids of the layer from which every feature is checked for overlap)
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.
- list of features
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(';')`