id-area-keys

areaKeys

This package contains the areaKeys data structure extracted from the OpenStreetMap iD Editor project.
Because of the open nature of OpenStreetMap tagging, iD will never have a complete list of tags used in OSM, so we want it to have logic like "assume that a closed way with an amenity tag is an area, unless the amenity is one of these specific types".
The areaKeys data structure allows testing of such conditions.
The returned object L is a keeplist/discardlist of tags. A closed way with a tag (k, v) is assumed to be an area if k in L && !(v in L[k]) (see iD.osmWay#isArea()).
In other words, the keys of L form the keeplist, and the subkeys form the discardlist.

Example:

In this subset of the areaKeys data structure, we can see that any closed ways with landuse=* or leisure=* are probably area features. But closed way exceptions like leisure=slipway or leisure=track are probably linear features.

{
  "areaKeys": {
    ...
    "landuse": { },
    "leisure": {
      "slipway": true,
      "track": true
    },
    ...
  }
}

isArea

This package also includes isArea utility function for testing an OpenStreetMap object against the area list. The isArea function accepts an Object of tags, and returns true if those tags imply an area feature, or false if those tags imply a linear feature.

Example:

const ak = require('id-area-keys');

ak.isArea({ 'natural': 'wood' });
// true - a closed way tagged `natural=wood` is an area filled with trees

ak.isArea({ 'natural': 'tree_row' });
// false - a closed way tagged `natural=tree_row` is a linear ring of trees

area=yes / area=no

In OpenStreetMap, an area tag can be used to force or disambiguate whether a closed way should be treated as a filled area (area=yes) or as a linear ring (area=no).
Because area tags override the other tags, an area key does not appear in areaKeys data structure, and users of this library must either handle area=yes/area=no tags in their own code, or use this library's exported isArea function, which does contain code to handle area=yes/area=no.

License

id-area-keys is available under the ISC License.

Version

To keep things simple, the released version of id-area-keys is pinned to a recently released version of the iD presets.