/usr/lib64/python2.4/site-packages/numpy/core/ma.py:604: UserWarning: Cannot automatically convert masked array to numeric because data
    is masked in one or more locations.
  warnings.warn("Cannot automatically convert masked array to "\
Traceback (most recent call last):
  File "./generate-worldmap.py", line 205, in ?
    sys.exit(main())
  File "./generate-worldmap.py", line 200, in main
    draw_client_density(r)
  File "./generate-worldmap.py", line 50, in draw_client_density
    colorbar(cax=cax,format=JefFormatter()) # draw colorbar
  File "/usr/lib64/python2.4/site-packages/matplotlib/pylab.py", line 324, in colorbar
    ret = gcf().colorbar(mappable, cax = cax, **kw)
  File "/usr/lib64/python2.4/site-packages/matplotlib/figure.py", line 766, in colorbar
    cb = cbar.Colorbar(cax, mappable, **kw)
  File "/usr/lib64/python2.4/site-packages/matplotlib/colorbar.py", line 501, in __init__
    ColorbarBase.__init__(self, ax, **kw)
  File "/usr/lib64/python2.4/site-packages/matplotlib/colorbar.py", line 161, in __init__
    self.draw_all()
  File "/usr/lib64/python2.4/site-packages/matplotlib/colorbar.py", line 172, in draw_all
    self._config_axes(X, Y)
  File "/usr/lib64/python2.4/site-packages/matplotlib/colorbar.py", line 196, in _config_axes
    ticks, ticklabels, offset_string = self._ticker()
  File "/usr/lib64/python2.4/site-packages/matplotlib/colorbar.py", line 314, in _ticker
    b, ticks = self._locate(b)
  File "/usr/lib64/python2.4/site-packages/matplotlib/colorbar.py", line 454, in _locate
    b = self.norm(self._boundaries, clip=False).filled()
  File "/usr/lib64/python2.4/site-packages/matplotlib/colors.py", line 658, in __call__
    raise ValueError("minvalue must be less than or equal to maxvalue")
ValueError: minvalue must be less than or equal to maxvalue