ggincerta (version 0.1.0)

StatPixel: Generate pixel maps on sf objects

Description

geom_sf_pixel() adds a pixel map layer based on simple feature (sf) objects to a ggplot. In a pixel map, each region is divided into small pixels, with colours mapped from values sampled from distribution specified.

Usage

StatPixel
geom_sf_pixel(
  mapping = NULL,
  data = NULL,
  n = 40,
  distribution = "uniform",
  seed = NULL,
  na.rm = FALSE,
  show.legend = NA,
  inherit.aes = TRUE,
  ...
)

Value

A list of ggplot2 layer objects.

Format

An object of class StatPixel (inherits from StatSf, Stat, ggproto, gg) of length 3.

Arguments

mapping

Set of aesthetic mappings created by ggplot2::aes(). v1 and v2 are required, which are the variables used as the parameters in the sampling distribution.

data

The data to be displayed in this layer. There are three options:

If NULL, the default, the data is inherited from the plot data as specified in the call to ggplot().

A data.frame, or other object, will override the plot data. All objects will be fortified to produce a data frame. See fortify() for which variables will be created.

A function will be called with a single argument, the plot data. The return value must be a data.frame, and will be used as the layer data. A function can be created from a formula (e.g. ~ head(.x, 10)).

n

integer of length 1 or 2, number of grid cells in x and y direction (columns, rows)

distribution

Sampling distribution: "uniform"(the default) or, "normal".

• "uniform" treats v1 as the centre and uniformly samples within the range (v1 - v2, v1 + v2).

• "normal" treats v1 as the mean and v2 as the standard deviation.

seed

Random seed used to ensure reproducibility of the sampling process.

na.rm

If FALSE, the default, missing values are removed with a warning. If TRUE, missing values are silently removed.

show.legend

logical. Should this layer be included in the legends? NA, the default, includes if any aesthetics are mapped. FALSE never includes, and TRUE always includes.

You can also set this to one of "polygon", "line", and "point" to override the default legend.

inherit.aes

If FALSE, overrides the default aesthetics, rather than combining with them. This is most useful for helper functions that define both data and aesthetics and shouldn't inherit behaviour from the default plot specification, e.g. annotation_borders().

...

Other arguments passed on to layer()'s params argument. These arguments broadly fall into one of 4 categories below. Notably, further arguments to the position argument, or aesthetics that are required can not be passed through .... Unknown arguments that are not part of the 4 categories below are ignored.

• Static aesthetics that are not mapped to a scale, but are at a fixed value and apply to the layer as a whole. For example, colour = "red" or linewidth = 3. The geom's documentation has an Aesthetics section that lists the available options. The 'required' aesthetics cannot be passed on to the params. Please note that while passing unmapped aesthetics as vectors is technically possible, the order and required length is not guaranteed to be parallel to the input data.

• When constructing a layer using a stat_*() function, the ... argument can be used to pass on parameters to the geom part of the layer. An example of this is stat_density(geom = "area", outline.type = "both"). The geom's documentation lists which parameters it can accept.

• Inversely, when constructing a layer using a geom_*() function, the ... argument can be used to pass on parameters to the stat part of the layer. An example of this is geom_area(stat = "density", adjust = 0.5). The stat's documentation lists which parameters it can accept.

• The key_glyph argument of layer() may also be passed on through .... This can be one of the functions described as key glyphs, to change the display of the layer in the legend.

Pixel map layer contents

The layer returned by geom_sf_pixel() internally includes a scale object created by scale_fill_distiller(). Therefore, modifying the scale will trigger a message indicating that the scale for fill is being replaced.

Examples

# Basic pixel map
p <- ggplot(nc) + geom_sf_pixel(mapping = aes(v1 = value, v2 = sd), n = 20)

# Replacing the internal fill scale triggers a message
# ("Scale for fill is already present. Adding another scale for fill...")
p + scale_fill_distiller(palette = "Blues")