code: def encode_single_layer(out, features, zoom):
      
      precision = precision_for_zoom(zoom)
      fs = create_layer_feature_collection(features, precision)
      json.dump(fs, out)
docs: Encode a list of (WKB|shapely, property dict, id) features into a
      GeoJSON stream.
  
      If no id is available, pass in None
  
      Geometries in the features list are assumed to be lon, lats.