layer:
  id: "waterway"
  description: |
      OpenStreetMap [waterways](http://wiki.openstreetmap.org/wiki/Waterways) for higher zoom levels
      and Natural Earth rivers and lake centerlines for low zoom levels.
      Linestrings without a name or which are too short are filtered
      out at low zoom levels. Waterways do no not have a `subclass` field.
  buffer_size: 4
  fields:
    name: |
        The OSM [`name`](http://wiki.openstreetmap.org/wiki/Key:name) value of the waterway.
        The `name` field may be empty for NaturalEarth data or at lower zoom levels.
    class:
      description: |
        The original value of the [`waterway`](http://wiki.openstreetmap.org/wiki/Key:waterway) tag.
      values:
      - stream
      - river
      - canal
      - drain
      - ditch
  datasource:
    geometry_field: geometry
    query: (SELECT geometry, name, class FROM layer_waterway(!bbox!, z(!scale_denominator!))) AS t
schema:
  - ./merge_waterway.sql
  - ./waterway.sql
datasources:
  - type: imposm3
    mapping_file: ./mapping.yaml