title: plotting data on to a country map
body: <p>hey guys having trouble with vincent, im not sure exactly how to use it 
  So ive parsed some data from the UK house of commons petition site, and now have a list of countries and their corresponding number of votes into a certain petition and ive got the data from JSON to <code>('Austria', 40)</code> format </p>
  
  <p>Im using vincent to plot them onto a map with colour scaled to represent number of votes but dont really know how to use vincent </p>
  
  <p>for example 
  to render a basic map of the world the code is</p>
  
  <pre><code>world_topo = r'world-countries.topo.json'
  geo_data = [{'name': 'countries',
               'url': world_topo,
               'feature': 'world-countries'}]
  
  vis = Map(geo_data=geo_data, scale=200)
  vis.to_json('vega.json')
  </code></pre>
  
  <p>but that just outputs a JSON, not a picture of a map, even though that is what two tutorial examples are saying should happen (for example here: <a href="http://wrobstory.github.io/2013/10/mapping-data-python.html" rel="nofollow">http://wrobstory.github.io/2013/10/mapping-data-python.html</a> and another place I forgot to save the link) </p>
  
  <p>could someone help me out? thanks in advance guys </p>