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contourPlot2 plots a contour map of a given quantity, such as the ground concentration of an airborne pollutant or odour, defined on a regular grid.

Usage

contourPlot2(
  data,
  x = "x",
  y = "y",
  z = "z",
  domain = NULL,
  background = NULL,
  underlayer = NULL,
  overlayer = NULL,
  legend = NULL,
  levels = NULL,
  size = 0,
  fill = TRUE,
  tile = FALSE,
  transparency = 0.75,
  colors = NULL,
  bare = FALSE
)

Arguments

data

dataframe in long format, with three columns for Easting, Northing and values to be plotted.

x

name of the column with Easting data (default "x").

y

name of the column with Northing data (default "y").

z

name of the column with the values to be plotted (default "z").

domain

optional list with six numeric values defining the boundaries of the domain to be plotted: minimum X, maximum X, minimum Y, maximum Y, number of ticks on X axis, number of ticks on Y axis.

background

optional path to a png file to be plotted as the base map.

underlayer

optional list of layers to be plotted between base map and contour plot.

overlayer

optional list of layers to be plotted on top of the contour plot.

legend

optional title of the legend.

levels

numeric vector of levels for contour plot. If not set, automatic pretty levels are computed. If -Inf and Inf are used as the lowest and highest limits of the array, the lowest and highest bands are unbounded and the legend shows < and >= symbols.

size

thickness of the contour line.

fill

boolean (default TRUE). If TRUE the contour plot is filled with colour.

tile

boolean (default FALSE). If TRUE rectangular tiles are plotted.

transparency

transparency level of the contour plot between 0.0 (fully transparent) and 1.0 (fully opaque). Default = 0.75).

colors

colour palette for contour plot, as an array of colours.

bare

boolean (default FALSE). If TRUE only the bare plot is shown: axis, legend, titles and any other graphical element of the plot are removed.

Value

A ggplot2 object.

Details

This is a convenience function to plot contour levels of a scalar quantity such as pollutants computed by a dispersion model, with ggplot2 version >= 3.3.0.

Data are required to be on a regular grid, typically (but not necessarily) in UTM coordinates. The input dataframe has to be in long format, i.e. one line per value to be plotted. The names of the columns corresponding to x, y and z can be specified in the input parameters.

If tile = TRUE data are shown as they are, without any graphical interpolation required for contour plots. This is helpful when you want to visualise the raw data. Since version 2.4.0, when tile = TRUE the intervals include the lowest bound and exclude the highest bound: [min, max). Note: In previous version it was the opposite.

underlayer and overlayer layers are ggplot2 objects to be shown at different levels of the vertical stack of the plot. These are useful to show topographical information related to the plot, such as sources or receptors locations.

Examples

# Load example data in long format
data(volcano)
volcano3d <- reshape2::melt(volcano)
names(volcano3d) <- c("x", "y", "z")
# Contour plot with default options
v <- contourPlot2(volcano3d)
v


# Set levels, and properly format the legend title:
contourPlot2(volcano3d, 
             levels = c(-Inf, seq(100, 200, 20), Inf),
             legend = expression(PM[10]~"["~mu*g~m^-3~"]"))


# Sometimes, instead of a contour plot it is better to plot the original
# raster data, without any interpolation:
contourPlot2(volcano3d, 
             levels = c(-Inf, seq(100, 200, 20), Inf), 
             tile = TRUE)
#> Warning: Removed 292 rows containing missing values (`geom_raster()`).


# Since contourPlot2 returns a `ggplot2` object, you can add instructions as:
library(ggplot2)
v + ggtitle("Example volcano data") +
    labs(x = NULL, y = NULL)