GISTools (version 0.7-4)

auto.shading: auto.shading

Description

Creates an object of class shading automatically, given a choropleth variable to be mapped.

Usage

auto.shading(x, digits = 2, cutter = quantileCuts, n = 5, 
	params = NA, cols = brewer.pal(n, "Reds"))

Arguments

x

The variable to be mapped.

digits

The number of significant digits to round the class limits to.

cutter

Function used to create the break points. Can be user defined or a supplied cut function.

n

The number of classes. The should be one more than the number of break points.

params

Other parameters to be passed to the cut function.

cols

List of colours for shading each class. length(cols) should be equal to n.

Value

An object of class shading, having the following list elements:

breaks

Break points between choropleth classes. length(cols)

cols

Colours to shade in each class. length(cols) should be one more than length(breaks)

Details

Returns an object of class shading, as set out below:

See Also

choropleth,shading,choro.legend.

Examples

# Read in map data and compute a rate for mapping
sids <- readShapePoly(system.file("shapes/sids.shp", package="maptools")[1], 
	proj4string=CRS("+proj=longlat +ellps=clrk66"))
sids.rate=10000*sids$SID74/sids$BIR74
# Create the shading scheme,  plot a choropleth map and add a legend
shades = auto.shading(sids.rate,n=6)
choropleth(sids,sids.rate,shades)
choro.legend(-83.77,37.87,shades,fmt="%4.1f",title='Rate per 10,000')
# Now again with a different set of class intervals and colours
shades = auto.shading(sids.rate,n=6,cutter=rangeCuts,cols=brewer.pal(6,'Greens'))
choropleth(sids,sids.rate,shades)
choro.legend(-83.77,37.87,shades,fmt="%4.1f",title='Rate per 10,000')