A data.frame object containing the data to be plotted
context.id
The identifier of the column containing the context ids. Must
correspond to the context ids in poly
names
A list of variables in dataframe we want to plot
show.names
A list of names to be added to the plots
method
chooses the style to be passed to classIntervals. It can be "fixed", "sd", "equal", "pretty",
"quantile", "kmeans", "hclust", "bclust", "fisher", or "jenks". Default is "equal".
nbr
A numeric vector that specifies the number of intervals to be displayed on the shape file