script.js

var map = L.map('map').setView([37.7, -122.4], 10);

  // load a tile layer
L.tileLayer('https://stamen-tiles-{s}.a.ssl.fastly.net/toner/{z}/{x}/{y}{r}.{ext}', {
	attribution: 'Map tiles by <a href="http://stamen.com">Stamen Design</a>, <a href="http://creativecommons.org/licenses/by/3.0">CC BY 3.0</a> &mdash; Map data &copy; <a href="https://www.openstreetmap.org/copyright">OpenStreetMap</a> contributors',
	subdomains: 'abcd',
	minZoom: 0,
	maxZoom: 20,
	ext: 'png'
}).addTo(map);

var blackIcon = new L.Icon({
  iconUrl: 'https://raw.githubusercontent.com/pointhi/leaflet-color-markers/master/img/marker-icon-black.png',
  shadowUrl: 'https://cdnjs.cloudflare.com/ajax/libs/leaflet/0.7.7/images/marker-shadow.png',
  iconSize: [25, 41],
  iconAnchor: [12, 41],
  popupAnchor: [1, -34],
  shadowSize: [41, 41]
});

  // load GeoJSON from an external file
  $.getJSON("https://raw.githubusercontent.com/gbrunner/adv-python-for-gis-and-rs/master/Week%201/sf_crime.geojson",function(data){   
    // add GeoJSON layer to the map once the file is loaded
    
    L.geoJson(data,{
    pointToLayer: function(feature,latlng){
	  return L.marker(latlng,{icon: blackIcon});
    }
   }).addTo(map);
  });