SubplotGrid should be able to change labelsize the same as GeoAxes does.

[gepcel]

From what I test, GeoAxes can change labelsize, but SubplotGrid doesn't. For example:

fig, ax = pplt.subplots(proj='cyl')
ax.format(labelsize=30) # no effect
ax[0].format(labelsize=30) # can change fontsize to 30

[cvanelteren]

That should indeed not happen.