Re: [Matplotlib-users] How do I make a legend for Line2D objects in Basemap, colored using a colormap?

[Eric F. <ef...@ha...>]

Zane Selvans wrote:
> Zane Selvans <zane@...> writes:
> 
>> I'm plotting a bunch of lines on a map.  They're being colored  
>> according to the value of an attribute associated with the objects  
>> they represent, using a colormap.  However, I also need to create a  
>> colorbar to act as a legend, describing what the colors of the lines  
>> means, in terms of values associated with that attribute.
>>
>> What's the easiest way to do that?
> 
> I've found the matplotlib.colorbar.ColorbarBase class... and have been able to
> use matplotlib.colorbar.make_axes() to create a somewhat acceptable set of axes
> into which I can put a colorbar constructed from the same colormap that I'm
> using to color the lines I'm plotting.  However, I can't seem to get the tics
> and axes on the colorbar to correspond to the values associated with the colors
> - they only ever go from 0-1.  I want them to go from, for instance, 0-180
> (degrees) in 20 or 30 degree intervals.  It seemed like setting the keyword
> arguments in ColorbarBase(boundaries=[0,180]) or values=linspace(0,180,10) or
> something like that ought to have done the right thing... but no, and I don't
> see any documentation on how these keywords are supposed to be used, in the
> docstring or elsewhere... anyone know how they work?

You probably want to use the ColorbarBase.add_lines() method; you can 
get an example of its use for line contours in the Colorbar class, and 
an example of the result is in examples/pylab_examples/contour_demo.py.

Eric