Polar frequency plots on dynamic and static maps

The freqMap() function creates a map using polar frequency plots as markers. Any number of pollutants can be specified using the pollutant argument, and multiple layers of markers can be created using type. By default, these maps are dynamic and can be panned, zoomed, and otherwise interacted with. Using the static argument allows for static images to be produced instead.

Usage

freqMap(
  data,
  pollutant = NULL,
  statistic = "mean",
  breaks = "free",
  latitude = NULL,
  longitude = NULL,
  crs = 4326,
  type = NULL,
  popup = NULL,
  label = NULL,
  provider = "OpenStreetMap",
  cols = "turbo",
  alpha = 1,
  key = FALSE,
  legend = TRUE,
  legend.position = NULL,
  legend.title = NULL,
  legend.title.autotext = TRUE,
  control.collapsed = FALSE,
  control.position = "topright",
  control.autotext = TRUE,
  d.icon = 200,
  d.fig = 3.5,
  static = FALSE,
  static.nrow = NULL,
  progress = TRUE,
  n.core = 1L,
  ...,
  control = NULL
)

Arguments

data

Input data table with pollutant, wind, and geo-spatial information.

required | scope: dynamic & static

A data frame. The data frame must contain the data to plot the directional analysis marker, which includes wind speed (ws), wind direction (wd), and the column representing the concentration of a pollutant. In addition, data must include a decimal latitude and longitude (or X/Y coordinate used in conjunction with crs).

pollutant

Pollutant name(s).

required | scope: dynamic & static

The column name(s) of the pollutant(s) to plot. If multiple pollutants are specified and a non-pairwise statistic is supplied, the type argument will no longer be able to be used and:

Dynamic: The pollutants can be toggled between using a "layer control" menu.
Static:: The pollutants will each appear in a different panel.

Multiple pollutants prohibit the use of the type argument for non-pairwise statistics.

statistic

The statistic that should be applied to each wind speed/direction bin.

default: "mean" | scope: dynamic & static

Can be "frequency", "mean", "median", "max" (maximum), "stdev" (standard deviation) or "weighted.mean". The option "frequency" is the simplest and plots the frequency of wind speed/direction in different bins. The scale therefore shows the counts in each bin. The option "mean" (the default) will plot the mean concentration of a pollutant (see next point) in wind speed/direction bins, and so on. Finally, "weighted.mean" will plot the concentration of a pollutant weighted by wind speed/direction. Each segment therefore provides the percentage overall contribution to the total concentration. Note that for options other than "frequency", it is necessary to also provide the name of a pollutant. See function openair::cutData() for further details.

breaks

Specifier for the breaks of the plot colour scale.

default: "free" | scope: dynamic & static

One of:

"fixed" which ensures all of the markers use the same colour scale.
"free" (the default) which allows all of the markers to use different colour scales.
A numeric vector defining a sequence of numbers to use as the breaks. The sequence could represent one with equal spacing, e.g., breaks = seq(0, 100, 10) - a scale from 0-10 in intervals of 10, or a more flexible sequence, e.g., breaks = c(0, 1, 5, 7, 10), which may be useful for some situations.

latitude, longitude

The decimal latitude(Y)/longitude(X).

default: NULL | scope: dynamic & static

Column names representing the decimal latitude and longitude (or other Y/X coordinate if using a different crs). If not provided, will be automatically inferred from data by looking for a column named "lat"/"latitude" or "lon"/"lng"/"long"/"longitude" (case-insensitively).

crs

The coordinate reference system (CRS).

default: 4326 | scope: dynamic & static

The coordinate reference system (CRS) of the data, passed to sf::st_crs(). By default this is EPSG:4326, the CRS associated with the commonly used latitude and longitude coordinates. Different coordinate systems can be specified using crs (e.g., crs = 27700 for the British National Grid). Note that non-lat/lng coordinate systems will be re-projected to EPSG:4326 for plotting on the map.

type

A method to condition the data for separate plotting.

default: NULL | scope: dynamic & static

Used for splitting the input data into different groups, passed to the type argument of openair::cutData(). When type is specified:

Dynamic: The different data splits can be toggled between using a "layer control" menu.
Static:: The data splits will each appear in a different panel.

type cannot be used if multiple pollutant columns have been provided.

popup

Content for marker popups on dynamic maps.

default: NULL | scope: dynamic

Columns to be used as the HTML content for marker popups on dynamic maps. Popups may be useful to show information about the individual sites (e.g., site names, codes, types, etc.). If a vector of column names are provided they are passed to buildPopup() using its default values.

label

Content for marker hover-over on dynamic maps.

default: NULL | scope: dynamic

Column to be used as the HTML content for hover-over labels. Labels are useful for the same reasons as popups, though are typically shorter.

provider

The basemap(s) to be used.

default: "OpenStreetMap" | scope: dynamic & static

The base map(s) to be used beneath the polar markers. If not provided, will default to "OpenStreetMap"/"osm" for both dynamic and static maps.

Dynamic: Any number of leaflet::providers. See http://leaflet-extras.github.io/leaflet-providers/preview/ for a list of all base maps that can be used. If multiple base maps are provided, they can be toggled between using a "layer control" interface. By default, the interface will use the provider names as labels, but users can define their own using a named vector (e.g., c("Default" = "OpenStreetMap", "Satellite" = "Esri.WorldImagery"))
Static: One of rosm::osm.types().

There is some overlap in static and dynamic providers. For example, {ggspatial} uses "osm" to specify "OpenStreetMap". When static providers are provided to dynamic maps or vice versa, {openairmaps} will attempt to substitute the correct provider string.

cols

Colours to use for plotting.

default: "turbo" | scope: dynamic & static

The colours used for plotting, passed to openair::openColours(). The default, "turbo", is a rainbow palette with relatively perceptually uniform colours.

alpha

Transparency value for polar markers.

default: 1 | scope: dynamic & static

A value between 0 (fully transparent) and 1 (fully opaque).

key

Draw individual marker legends?

default: FALSE | scope: dynamic & static

Draw a key for each individual marker? Potentially useful when limits = "free", but of limited use otherwise.

legend

Draw a shared legend?

default: TRUE | scope: dynamic & static

When all markers share the same colour scale (e.g., when limits != "free" in polarMap()), should a shared legend be created at the side of the map?

legend.position

Position of the shared legend.

default: NULL | scope: dynamic & static

When legend = TRUE, where should the legend be placed?

Dynamic: One of "topright", "topright", "bottomleft" or "bottomright". Passed to the position argument of leaflet::addLegend().
Static:: One of "top", "right", "bottom" or "left". Passed to the legend.position argument of ggplot2::theme().

legend.title

Title of the legend.

default: NULL | scope: dynamic & static

By default, when legend.title = NULL, the function will attempt to provide a sensible legend title. legend.title allows users to overwrite this - for example, to include units or other contextual information. For dynamic maps, users may wish to use HTML tags to format the title.

legend.title.autotext

Automatically format the title of the legend?

default: TRUE | scope: dynamic & static

When legend.title.autotext = TRUE, legend.title will be first run through quickTextHTML() (dynamic) or openair::quickText() (static).

control.collapsed

Show the layer control as a collapsed?

default: FALSE | scope: dynamic

For dynamic maps, should the "layer control" interface be collapsed? If TRUE, users will have to hover over an icon to view the options.

control.position

Position of the layer control menu

default: "topright" | scope: dynamic

When type != NULL, or multiple pollutants are specified, where should the "layer control" interface be placed? One of "topleft", "topright", "bottomleft" or "bottomright". Passed to the position argument of leaflet::addLayersControl().

control.autotext

Automatically format the content of the layer control menu?

default: TRUE | scope: dynamic

When control.autotext = TRUE, the content of the "layer control" interface will be first run through quickTextHTML().

d.icon

The diameter of the plot on the map in pixels.

default: 200 | scope: dynamic & static

This will affect the size of the individual polar markers. Alternatively, a vector in the form c(width, height) can be provided if a non-circular marker is desired.

d.fig

The diameter of the plots to be produced using {openair} in inches.

default: 3.5 | scope: dynamic & static

This will affect the resolution of the markers on the map. Alternatively, a vector in the form c(width, height) can be provided if a non-circular marker is desired.

static

Produce a static map?

default: FALSE

This controls whether a dynamic or static map is produced. The former is the default and is broadly more useful, but the latter may be preferable for DOCX or PDF outputs (e.g., academic papers).

static.nrow

Number of rows in a static map.

default: NULL | scope: static

Controls the number of rows of panels on a static map when multiple pollutants or type are specified; passed to the nrow argument of ggplot2::facet_wrap(). The default, NULL, results in a roughly square grid of panels.

progress

Show a progress bar?

default: TRUE | scope: dynamic & static

By default, a progress bar is shown to visualise the function's progress creating individual polar markers. This option allows this to be turned off, if desired.

n.core

Number of cores to use in parallel processing.

default: 1L | scope: dynamic & static

By default, each polar marker is drawn and saved sequentially. For big maps with a lot of markers, this can be slow. Adjusting n.core to a number greater than 1 will use mirai to create markers in parallel.

...

Arguments passed on to openair::polarFreq

ws.int: Wind speed interval assumed. In some cases e.g. a low met mast, an interval of 0.5 may be more appropriate.
wd.nint: Number of intervals of wind direction.
grid.line: Radial spacing of grid lines.
trans: Should a transformation be applied? Sometimes when producing plots of this kind they can be dominated by a few high points. The default therefore is TRUE and a square-root transform is applied. This results in a non-linear scale and (usually) a better representation of the distribution. If set to FALSE a linear scale is used.
min.bin: The minimum number of points allowed in a wind speed/wind direction bin. The default is 1. A value of two requires at least 2 valid records in each bin an so on; bins with less than 2 valid records are set to NA. Care should be taken when using a value > 1 because of the risk of removing real data points. It is recommended to consider your data with care. Also, the polarFreq function can be of use in such circumstances.
ws.upper: A user-defined upper wind speed to use. This is useful for ensuring a consistent scale between different plots. For example, to always ensure that wind speeds are displayed between 1-10, set ws.int = 10.
offset: offset controls the size of the ‘hole’ in the middle and is expressed as a percentage of the maximum wind speed. Setting a higher offset e.g. 50 is useful for statistic = "weighted.mean" when ws.int is greater than the maximum wind speed. See example below.
border.col: The colour of the boundary of each wind speed/direction bin. The default is transparent. Another useful choice sometimes is "white".
key.header: Adds additional text/labels to the scale key. For example, passing the options key.header = "header", key.footer = "footer1" adds addition text above and below the scale key. These arguments are passed to drawOpenKey via quickText, applying the auto.text argument, to handle formatting.
key.footer: see key.footer.
key.position: Location where the scale key is to plotted. Allowed arguments currently include "top", "right", "bottom" and "left".
auto.text: Either TRUE (default) or FALSE. If TRUE titles and axis labels will automatically try and format pollutant names and units properly e.g. by subscripting the `2' in NO2.

control

Deprecated. Please use type.

Value

Either:

Dynamic: A leaflet object
Static: A ggplot2 object using ggplot2::coord_sf() coordinates with a ggspatial basemap

Customisation of static maps using ggplot2

As the outputs of the static directional analysis functions are ggplot2 figures, further customisation is possible using functions such as ggplot2::theme(), ggplot2::guides() and ggplot2::labs().

If multiple pollutants are specified, subscripting (e.g., the "x" in "NOx") is achieved using the ggtext package. Therefore if you choose to override the plot theme, it is recommended to use [ggplot2::theme()] and [ggtext::element_markdown()] to define the strip.text parameter.

When arguments like limits, percentile or breaks are defined, a legend is automatically added to the figure. Legends can be removed using ggplot2::theme(legend.position = "none"), or further customised using ggplot2::guides() and either color = ggplot2::guide_colourbar() for continuous legends or fill = ggplot2::guide_legend() for discrete legends.

Examples

if (FALSE) { # \dontrun{
freqMap(polar_data,
  pollutant = "nox",
  statistic = "mean",
  provider = "CartoDB.Voyager"
)
} # }

Polar frequency plots on dynamic and static maps

Usage

Arguments

Value

Customisation of static maps using ggplot2

See also

Examples