title: How to plot Latitude and Longitude in Bokeh
body: <p>I have created a figure in bokeh with X and Y axis labels showing latitude and longitude coordinates but using a WMTS tile map which of course uses Mercator projection.  I presume there is some kind of conversion taking place by Bokeh since in their documentation they say:</p>
  
  <p>"Notice also that passing x_axis_type="mercator" and y_axis_type="mercator" to figure generate axes with latitude and longitude labels, instead of raw Web Mercator coordinates"
  (<a href="https://docs.bokeh.org/en/latest/docs/user_guide/geo.html" rel="nofollow noreferrer">https://docs.bokeh.org/en/latest/docs/user_guide/geo.html</a>)</p>
  
  <p>When I plot markers however, which are set by LAT and LON they ignore the X and Y axis scale and instead plot according to Mercator scale</p>
  
  <pre><code>title = "test"
  
  mercator_extent = dict(start=-20000000, end=20000000,bounds=None)
  
  # create a tile source
  tile_options = {}
  tile_options['url'] = 'http://tile.stamen.com/watercolor/{z}/{x}/{y}.jpg'
  tile_options['attribution'] = """
      Map tiles by &lt;a href="http://stamen.com"&gt;Stamen Design&lt;/a&gt;, under
      &lt;a href="http://creativecommons.org/licenses/by/3.0"&gt;CC BY 3.0&lt;/a&gt;.
      Data by &lt;a href="http://openstreetmap.org"&gt;OpenStreetMap&lt;/a&gt;,
      under &lt;a href="http://www.openstreetmap.org/copyright"&gt;ODbL&lt;/a&gt;.
      """
  
  mq_tile_source = WMTSTileSource(**tile_options)
  
  source = ColumnDataSource(data=OrderedDict(lat=([50]), lon=([50])))
  
  x_range= Range1d(**mercator_extent)
  y_range= Range1d(**mercator_extent)
  
  plot = figure(title='printed line on map',
                tools= "pan,wheel_zoom",
                x_range=x_range,
                x_axis_type="mercator",
                y_axis_type="mercator",
                y_range=y_range,
                sizing_mode = 'stretch_both')#create a figure
  
  plot.add_tile(mq_tile_source)#add the map
  
  plot.circle(source=source,x='lon',y='lat',line_color ='red')
  
  output_file("file.html")
  save(plot)
  </code></pre>
  
  <p>I am under the impression that setting X and Y axis = "mercator" my X and Y axis labels are shown as latitude and longitude and therefore my markers should plot against the axis accordingly.  In other words, according the the example above i should have marker that observes that X and Y axis but I don't.  </p>
  
  <p>Image below shows the output; the hover tool shows my data is 50 LAT and LON and so I would expect the marker to be where i have manually drawn a purple blob but instead it plots almost dead center</p>
  
  <p><a href="https://i.stack.imgur.com/nElaa.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/nElaa.jpg" alt="enter image description here"></a></p>
  
  <p>any idea?</p>