[BUG/ISSUE] Display of all zeros in colorbar

[lizziel]

We have had two different ways of conveying that all displayed values are zero. One is to show multiple zeroes spanning the entire colorbar.

Another is to show a single zero in the middle with the bounds of the colorbar unlabeled (current).

It would be good to get some feedback on preference. I prefer multiple zeroes since then there is no doubt about the range, but others may disagree.

[yantosca]

For me, seeing a single tickmark at zero immediately tells me that the difference is zero. That is quicker than having to look at the whole colorbar to realize that all of the ticmarks are zero. For what it's worth...

[sdeastham]

How about making it more explicit, and changing the single tickmark to read "No change in domain" or "Zero throughout domain"? It's wordy, but it's completely explicit and should be easy to program. Once you have the colorbar (say cb = plt.colorbar()), I think the following would do it:

cb.set_yticks([0])
cb.ax.set_yticklabels(['Zero throughout domain'])

[yantosca]

I've now added a tickmark with "Zero throughout domain" to commit #aa95a343. We can still change the tick label if need be but this makes it explicit.

For the record, I had to use:

cb.set_ticks([0.5])
cb.set_ticklabels(['Zero throughout domain'])

i..e. not set_yticks and set_yticklabels. Also because the normalized color range is now 0 to 1, we are plotting the tickmark at 0.5 in the center. This also makes the zero color show up as white, which is what we wanted.