Streaming conversion of National Weather Service alerts to GeoJSON

geojson.stream() is a through-stream that converts alerts into geojson FeatureCollections. It is intended to be used downstream of weather-alerts-parser. Each alert will be converted to a separate feature collection.

The stylize option will add simple styles based on the official NWS hazard map colors.

geojson.collect() will a convert a stream of alert FeatureCollections into a single FeatureCollection where each feature (e.g. a specific county) contains all the alerts that apply to it in the properties attribute.

By default, properties will be an array containing these alerts, but if flatten option is set to true, then properties will be a JSON object containing the alert properties. If there is only one alert, then those attributes will be directly available on properties. If there is more than one alert, then properties will contain an alert-count attribute and for each alert, the alert properties will be prefixed with alert-<N>- where N is the index (starting at 1) of the each alert's properties. Putting properties into a single flat object is a little more standard and will probably be supported in more tools/environs.

If the sort option is set to true, then alerts will be sorted by severity, urgency, and certainty. More severe alerts will be first, if there is a tie in severity then more urgent alerts will be first. If severity and urgency are the same, then certainty is used to break any ties there.

Here's an example that writes a GeoJSON FeatureCollection representing the current alerts to stdout:

var es = require('event-stream');
var geojson = require('weather-alerts-geojson');
var parser = require('weather-alerts-parser');
var request = require('request');

request.get('http://alerts.weather.gov/cap/us.php?x=1')
  .pipe(parser.stream())
  .pipe(geojson.stream({'stylize': true}))
  .pipe(geojson.collect({'sort': true, 'flatten': true}))
  .pipe(es.stringify())
  .pipe(process.stdout)