anchor.diff:  
           var key = "bibs"; // defined in _header.html.erb
           var selected_racers = JSON.parse(localStorage.getItem(key)); // view _header to see how bibs are stored
  -        var racer_markers = [];
  +        var racer_markers = []; // array of markers that are displayed on map
   
           // initialize markers for selected racers so locations can be updated
           var n;
  
positive.code: <!-- include cartodb.js library -->
  <script src="http://libs.cartocdn.com/cartodb.js/v3/3.15/cartodb.js"></script>
  
  <div id="map"></div>
  
  <script>
      function main() {
          var southWest = L.latLng(-90, 180),
                  northEast = L.latLng(90, -180),
                  bounds = L.latLngBounds(southWest, northEast);
  
          var map = L.map('map', {
              scrollWheelZoom: false,
              center: [40.7127837, -74.0059413],
              zoom: 3
          });
  
          var layer = L.tileLayer('http://{s}.basemaps.cartocdn.com/light_all/{z}/{x}/{y}@2x.png', {
              bounds: bounds,
  
negative.code:         }
  
          // use json located in content from html to update coordinates for racers
          // Precondition: html page has json with racer information contained in div specified by JSON_DIV_ID
          //               selected_racers and racer_markers are of the same length
          function plotCoords(html) {
              var JSON_DIV_ID = "div#racers_info";
  
              // obtain racers information contained in div
              var tmp = jQuery('<div>').html(html);
              var racers_json = JSON.parse( tmp.find(JSON_DIV_ID).html() );
              selected_racers = JSON.parse(localStorage.getItem(key)); // view _header to see how bibs are stored
  
              // update markers for selected racers on map
              var i;
  