Axes flipped when plotting an xarray.DataArray

[maawoo]

ALL software version info

• Python 3.9.7 conda environment on CentOS 7
• hvplot=0.7.3
• holoviews=1.14.5
• datashader=0.13
• xarray=0.19

hvplot imported as import hvplot.xarray

Description of expected behavior and the observed behavior

Expected:
Plot created from a 2-dimensional xarray.DataArray is by default plotted similarly to xarray's matplotlib wrapper, i.e. same orientation of axes.

Observed:
x and y axes are flipped

Complete, minimal, self-contained example code that reproduces the issue

Can't provide a self-contained example but hopefully the following helps.

The xarray.DataArray with UTM x and y coordinates:

Plot using xarray's matplotlib wrapper showing the correct orientation:

ds.plot(cmap='viridis', figsize=(12, 10))

Plots using hvplot (same problem with .hvplot and .hvplot.image) with some flippin' going on:

ds.hvplot(cmap='viridis', height=600, width=800) 
ds.hvplot.image(cmap='viridis', height=600, width=800)

[maawoo]

Okay solved it myself by passing x='x', y='y'. I misunderstood this earlier and tried passing x=ds.x, y=ds.y instead, which doesn't work. Shouldn't x='x', y='y' be the default, however?

[philippjfr]

Thanks for the issue!

Shouldn't x='x', y='y' be the default, however?

I'd prefer not to add any special case logic looking for specific coordinate names so definitely -1 on that. However since xarray somehow figures out the appropriate axis ordering in this case we will have to take another look at how they do it compared to how we do it.

[maximlt]

xarray reverses the DataArray dims, it considers the x-axis as dims[1] and and the y-axis as dims[0].

This is defined here:
https://github.com/pydata/xarray/blob/f8bae5974ee2c3f67346298da12621af4cae8cf8/xarray/plot/utils.py#L376

In the example provided by the OP the DataArray dimensions are ('y', 'x') so when reversed they are "correctly" displayed. I don't know if this inversion done by xarray lies on some sort of convention but without any more context (no attributes parsing or anything else), it seems to me it's a little too arbitrary, and anyway easily handled at the hvplot level with x='x', y='y'. I'm going to close this issue then, if this happens to rely on a convention I was not aware please let me know and I'll happily implement xarray's behavior.

[maximlt]

@philippjfr should we reproduce what xarray does, as asked in this issue?