choroLayer {cartography} R Documentation

## Choropleth Layer

### Description

Plot a choropleth layer.

### Usage

choroLayer(
x,
spdf,
df,
spdfid = NULL,
dfid = NULL,
var,
breaks = NULL,
method = "quantile",
nclass = NULL,
col = NULL,
border = "grey20",
lwd = 1,
colNA = "white",
legend.pos = "bottomleft",
legend.title.txt = var,
legend.title.cex = 0.8,
legend.values.cex = 0.6,
legend.values.rnd = 0,
legend.nodata = "no data",
legend.frame = FALSE,
legend.border = "black",
legend.horiz = FALSE,
)


### Arguments

 x an sf object, a simple feature collection. If x is used then spdf, df, spdfid and dfid are not. spdf a SpatialPolygonsDataFrame. df a data frame that contains the values to plot. If df is missing spdf@data is used instead. spdfid name of the identifier variable in spdf, default to the first column of the spdf data frame. (optional) dfid name of the identifier variable in df, default to the first column of df. (optional) var name of the numeric variable to plot. breaks break values in sorted order to indicate the intervals for assigning the colors. Note that if there are nlevel colors (classes) there should be (nlevel+1) break values (see Details). method a classification method; one of "sd", "equal", "quantile", "fisher-jenks","q6", "geom", "arith", "em" or "msd" (see getBreaks). nclass a targeted number of classes. If null, the number of class is automatically defined (see Details). col a vector of colors. Note that if breaks is specified there must be one less colors specified than the number of break. border color of the polygons borders. lwd borders width. colNA no data color. legend.pos position of the legend, one of "topleft", "top", "topright", "right", "bottomright", "bottom", "bottomleft", "left" or a vector of two coordinates in map units (c(x, y)). If legend.pos is "n" then the legend is not plotted. legend.title.txt title of the legend. legend.title.cex size of the legend title. legend.values.cex size of the values in the legend. legend.values.rnd number of decimal places of the values in the legend. legend.nodata no data label. legend.frame whether to add a frame to the legend (TRUE) or not (FALSE). legend.border color of boxes borders in the legend. legend.horiz whether to display the legend horizontally (TRUE) or not (FALSE). add whether to add the layer to an existing plot (TRUE) or not (FALSE).

### Details

The optimum number of class depends on the number of geographical objects. If nclass is not defined, an automatic method inspired by Sturges (1926) is used : nclass = 1+3.3*log10(N), where nclass is the number of class and N is the variable length.

If breaks is used then nclass and method are not.

If breaks is defined as c(2, 5, 10, 15, 20) intervals will be: [2 - 5[, [5 - 10[, [10 - 15[, [15 - 20].

### References

Herbert A. Sturges, « The Choice of a Class Interval », Journal of the American Statistical Association, vol. 21, n° 153, mars 1926, p. 65-66.

### Examples

library(sf)
# Population density
mtq$POPDENS <- 1e6 * mtq$POP / st_area(x = mtq)

# Default
choroLayer(x = mtq, var = "POPDENS")

# With parameters
choroLayer(x = mtq, var = "POPDENS",
method = "quantile", nclass = 5,
col = carto.pal(pal1 = "sand.pal", n1 = 5),
border = "grey40",
legend.pos = "topright", legend.values.rnd = 0,
legend.title.txt = "Population Density\n(people per km2)")

# Layout
layoutLayer(title = "Population Distribution in Martinique, 2015")


[Package cartography version 3.0.1 Index]