title: Blank/grey folium map when rendering in Jupyter Notebooks
body: <p>everyone. It's my first time here. </p>
  
  <p>I'm trying to create a choropleth map that shows San Francisco's crime rate. I think that the code was just correct but for some reason, the map is not rendering. I can see the zoom buttons, the gauge, and the legend but not the map. I am only seeing a blank grey background. I had this problem with Jupyter Notebooks, Google Colab, and IBM Watson Studio.</p>
  
  <p>Here's the screenshot of the rendered map and the code that I wrote. Behind the image, it tells me to make the notebook Trusted. But I think that the notebook is trusted because I created it (and Jupyter tells it). Some references said that it's because of the browser but the same thing happens in Chrome and Firefox. I tried creating a simple world map (using <code>world_map = folium.map(); world_map</code>) but it successfully rendered the world map. </p>
  
  <p>I'm not sure what to do next. Any suggestions will be much appreciated. Thanks.</p>
  
  <p><a href="https://i.stack.imgur.com/8JEWV.png" rel="nofollow noreferrer">rendered map - grey screen</a></p>
  
  <pre><code>#create pandas dataframe
  crime = pd.read_csv('https://cocl.us/sanfran_crime_dataset')
  crime.rename({'PdDistrict':'Neighborhood'}, axis=1, inplace=True)
  crime_neighborhood = crime['Neighborhood'].value_counts().to_frame()
  crime_neighborhood.reset_index(level=0, inplace=True)
  crime_neighborhood.rename({'Neighborhood':'Count', 'index':'Neighborhood'}, inplace=True, axis=1)
  
  #import json 
  !wget --quiet https://cocl.us/sanfran_geojson/san-francisco.geojson -o san-francisco.geo.json
  sanfran_json = r'https://cocl.us/sanfran_geojson/san-francisco.geojson'
  
  #create San Francisco map
  sanfran_map = fl.Map(location=[38, 122], zoom_start=12, tiles='Mapbox Bright')
  
  #create Choropleth map
  fl.Choropleth(
      geo_data=sanfran_json,
      data=crime_neighborhood,
      columns=['Neighborhood', 'Count'],
      key_on='feature.properties.DISTRICT',
      fill_color='YlOrRd', 
      fill_opacity=0.7, 
      line_opacity=0.2,
      legend_name='San Francisco Crime Rate').add_to(sanfran_map)
  
  #show map
  sanfran_map
  </code></pre>