plotting STSDF objects

Hi,

I am using the spacetime package to create plots of disease spread across a
landscape.  I have a sparse dataframe and am having trouble using the
stplot function to show all of the spatial polygons in a sparse dataframe
(ie I would like to plot all the spatial polygons, even those representing
townships with no case reports during the time period).

I have used the following code:
stplot(stsdf[,,"lyme_cases"], t, col.regions = brewer.pal(9,
"YlOrRd"),cuts=9)

I was wondering if this was the correct syntax for stplot for an STSDF
object and also what exactly the "signature" means in the Methods section
of stplot:
signature(x = "STSDF"): plots object of class STSDF

Thank you very much for your help!
Best,

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