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Polar frequency plots on interactive leaflet maps

Source: R/polar_freqMap.R
freqMap.Rd

freqMap() creates a leaflet map using binned polar plots as markers. Any number of pollutants can be specified using the pollutant argument, and multiple layers of markers can be added and toggled between using control.

Usage

freqMap(
  data,
  pollutant = NULL,
  statistic = "mean",
  breaks = "free",
  latitude = NULL,
  longitude = NULL,
  control = NULL,
  popup = NULL,
  label = NULL,
  provider = "OpenStreetMap",
  cols = "turbo",
  alpha = 1,
  key = FALSE,
  draw.legend = TRUE,
  collapse.control = FALSE,
  d.icon = 200,
  d.fig = 3.5,
  type = deprecated(),
  ...
)

Arguments

data

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.

pollutant

The column name(s) of the pollutant(s) to plot. If multiple pollutants are specified, they can be toggled between using a "layer control" interface.

statistic

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

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/longitude. If not provided, will be automatically inferred from data by looking for a column named "lat"/"latitude" or "lon"/"lng"/"long"/"longitude" (case-insensitively).

control

Used for splitting the input data into different groups which can be selected between using a "layer control" interface, passed to the type argument of openair::cutData(). control cannot be used if multiple pollutant columns have been provided.

popup

Columns to be used as the HTML content for marker popups. 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

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 base map(s) to be used. 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"))

cols

The colours used for plotting. See openair::openColours() for more information.

alpha

The alpha transparency to use for the plotting surface (a value between 0 and 1 with zero being fully transparent and 1 fully opaque).

key

Should a key for each marker be drawn? Default is FALSE.

draw.legend

When breaks are specified, should a shared legend be created at the side of the map? Default is TRUE.

collapse.control

Should the "layer control" interface be collapsed? Defaults to FALSE.

d.icon

The diameter of the plot on the map in pixels. 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. 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.

type

[Deprecated]. Different sites are now automatically detected based on latitude and longitude. Please use label and/or popup to label different sites.

...

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.

Value

A leaflet object.

See also

the original openair::polarFreq()

freqMapStatic() for the static ggmap equivalent of freqMap()

Other interactive directional analysis maps: annulusMap(), diffMap(), percentileMap(), polarMap(), pollroseMap(), windroseMap()

Examples

if (FALSE) {
freqMap(polar_data,
  pollutant = "nox",
  statistic = "mean",
  provider = "Stamen.Toner"
)
}