docs: function getDistanceInKilometers(p1, p2) {
    // Credit: adapts code for Haversine formula and degrees-to-radian conversion found at:
    // http://www.movable-type.co.uk/scripts/latlong.html
  
    var R = 6371; // earth's radius in kilometers
    var dLat = degreesToRadians(p2.lat - p1.lat);
    var dLon = degreesToRadians(p2.lng - p1.lng); 
    var lat1 = degreesToRadians(p1.lat);
    var lat2 = degreesToRadians(p2.lat);
  
    var a = 
      Math.sin(dLat/2) * Math.sin(dLat/2)
      + Math.sin(dLon/2) * Math.sin(dLon/2)
      * Math.cos(lat1) * Math.cos(lat2);
  
    var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a)); 
    var distance = R * c; // kilomter
    return distance;
  }