title: Plotting discrete X/Y values over Seaborn heatmap
body: <p>I'm trying to mark a specific X/Y coordinate on a Seaborn heatmap.  The output is plotting the correct X coordinate but is plotting the Y as zero/axis minimum. Code and its heatmap output is shown below.</p>
  
  <pre><code>speeds = pd.read_csv('pytest20140730.csv') 
  speedspiv = pd.pivot_table(speeds, values = 'speed', index = 'road_order',
                             columns = 'tod_value', aggfunc = np.mean)
  speedspiv = speedspiv.sort_index(axis=0, ascending = False)
  plt.subplots(figsize=(20,15))
  ax = sns.heatmap(speedspiv)
  ax.scatter(414, 0.244444444, marker='*', s=100, color='yellow') 
  </code></pre>
  
  <p>See yellow star on x-axis of the following image
  <a href="https://i.stack.imgur.com/jni8i.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/jni8i.png" alt="enter image description here"></a></p>
  
  <p>What's up with the Y axis value not plotting correctly?</p>