highlight single contour line

Question

I'm making a simple contour plot and I want to highlight the zero line by making it thicker and changing the color.

cs = ax1.contour(x,y,obscc)
ax1.clabel(cs,inline=1,fontsize=8,fmt='%3.1f')

How do I achieve this? Thanks :-)

Answer 1

HTH -- this is basically the contour example taken from the matplotlib docs, just with modified level lines

The object that is returned from the contour-method holds a reference to the contour lines in its collections attribute. The contour lines are just common LineCollections.

In the following code snippet the reference to the contour plot is in CS (that is cs in your question):

CS.collections[0].set_linewidth(4)           # the dark blue line
CS.collections[2].set_linewidth(5)           # the cyan line, zero level
CS.collections[2].set_linestyle('dashed')
CS.collections[3].set_linewidth(7)           # the red line
CS.collections[3].set_color('red')
CS.collections[3].set_linestyle('dotted')

type(CS.collections[0])
# matplotlib.collections.LineCollection

Here's how to find out about the levels, if you didn't explicitly specify them:

CS.levels
array([-1. , -0.5,  0. ,  0.5,  1. ,  1.5])

There is also a lot of functionality to format individual labels:

CS.labelCValueList    CS.labelIndiceList    CS.labelTextsList
CS.labelCValues       CS.labelLevelList     CS.labelXYs
CS.labelFmt           CS.labelManual        CS.labels
CS.labelFontProps     CS.labelMappable      CS.layers
CS.labelFontSizeList  CS.labelTexts