title: (matpolotlib) ValueError: too many values to unpack
body: <p>I am getting the following error when trying to display data values instead of markers:</p>
  
  <p><strong>Complete Traceback:</strong></p>
  
  <pre><code>Traceback (most recent call last):
  File "plotpoints.py", line 45, in &lt;module&gt;
  plt.annotate(grid_x,grid_y)
  File "/usr/lib/pymodules/python2.7/matplotlib/pyplot.py", line 3405, in annotate
  ret = gca().annotate(*args, **kwargs)
  File "/usr/lib/pymodules/python2.7/matplotlib/axes.py", line 3404, in annotate
  a = mtext.Annotation(*args, **kwargs)
  File "/usr/lib/pymodules/python2.7/matplotlib/text.py", line 1813, in __init__
  annotation_clip=annotation_clip)
  File "/usr/lib/pymodules/python2.7/matplotlib/text.py", line 1442, in __init__
  x, y = self.xytext = xytext
  ValueError: too many values to unpack
  </code></pre>
  
  <p><strong>Code:</strong></p>
  
  <pre><code>m = mapformat()
  
  dx = 0.25
  
  grid_x, grid_y = np.mgrid[-85:64:dx, 34:49:dx]
  
  grid_z = griddata((data[:,1],data[:,0]), data[:,2], (grid_x,grid_y), method='linear')
  
  x,y = m(data[:,1], data[:,0]) # flip lat/lon
  
  grid_x,grid_y = m(grid_x,grid_y)
  
  plt.annotate(grid_x,grid_y)
  
  #m.plot(grid_x,grid_y, 'ko', markersize=2)
  </code></pre>
  
  <p>What am I doing wrong?</p>