Compute a GeoJSON of centroids for markets with stations using lodash and turf.js.

marketcoords.js

var turf = require('turf'),
    _ = require('lodash');

// iterate through markets
markets = markets.map(function (stations) {
    // and stations within those markets
    var transmitters = stations.map(function (station) {
        // reduce the stations to coordinates, or null
        if (station.fcc_station && station.fcc_station.transmitter && station.fcc_station.transmitter.coordinates) {
            return turf.point(station.fcc_station.transmitter.coordinates);
        }
        else {
            return null;
        }
    });

    // remove null locations, package into GeoJSON feature collection
    transmitters = turf.featurecollection(_.compact(transmitters));

    // compute centroid for market
    var centroid = turf.centroid(transmitters);

    // set properties on the market GeoJSON object, including a total, name and ID
    centroid.properties.id = stations[0].market;
    centroid.properties.name = stations[0].market;
    centroid.properties.total = _.sum(stations,'count');
    
    return centroid;
});

// package markets into GeoJSON feature collection
markets = turf.featurecollection(markets);