**Edit**: Since this seems to be a popular post, here&#39;s the solution that seems to be working well for me. Thanks @gazzar and @mfra.

    cbar.solids.set_rasterized(True)
    cbar.solids.set_edgecolor(&quot;face&quot;)

----

Does anyone know why my colorbar has what appear to be lines in it? Or rather why is the color transition not smooth? I&#39;m using basemap, obviously, but that shouldn&#39;t matter since it&#39;s all matplotlib calls under the hood AFAICT. I create the map doing something like

    grays = plt.cm.get_cmap(&quot;Grays&quot;)
    sc = mymap.scatter(xpoints, ypoints, s=sizes, c=color_values, cmap=grays, alpha=.75,
                       marker=&quot;o&quot;, zorder=10, vmin=0, vmax=1)
    cbar = mymap.colorbar(sc, drawedges=True, location=&quot;bottom&quot;)

I tried without and without alpha and the result was the same. Maybe it is because my color_values array is not fine enough? Can I set the underlying values that are mapped to the colorbar somewhere? I don&#39;t see how, and I don&#39;t see this problem elsewhere. Ie., I can replicate the matplotlib show_colorbars example without this problem.

![Bad Colorbar Example][1]
    


  [1]: http://i.stack.imgur.com/3Uq9v.png

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why does my colorbar have lines in it?