Trajectory line plots in ggplot2 — trajMapStatic • openairmaps

This function plots back trajectories using ggplot2. The function requires that data are imported using openair::importTraj(). It is a ggplot2 implementation of openair::trajPlot() with many of the same arguments, which should be more flexible for post-hoc changes.

Usage

trajMapStatic(
  data,
  colour = "height",
  facet = NULL,
  group = NULL,
  longitude = "lon",
  latitude = "lat",
  npoints = 12,
  xlim = NULL,
  ylim = NULL,
  crs = sf::st_crs(3812),
  origin = TRUE,
  map = TRUE,
  map.fill = "grey85",
  map.colour = "grey75",
  map.alpha = 0.8,
  map.lwd = 0.5,
  map.lty = 1,
  ...
)

Arguments

data

Data frame, the result of importing a trajectory file using openair::importTraj().

colour

Column to be used for colouring each trajectory. This column may be numeric, character or factor. This will commonly be a pollutant concentration which has been joined (e.g., by dplyr::left_join()) to the trajectory data by "date".

facet

Used for splitting the trajectories into different panels. Passed to openair::cutData().

group

By default, trajectory paths are distinguished using the arrival date. group allows for additional columns to be used (e.g., "receptor").

latitude, longitude

The decimal latitude/longitude.

npoints

A dot is placed every npoints along each full trajectory. For hourly back trajectories points are plotted every npoints hours. This helps to understand where the air masses were at particular times and get a feel for the speed of the air (points closer together correspond to slower moving air masses). Defaults to 12.

xlim, ylim

The x- and y-limits of the plot. If NULL, limits will be estimated based on the lat/lon ranges of the input data.

crs

The coordinate reference system (CRS) into which all data should be projected before plotting. Defaults to the Lambert projection (sf::st_crs(3812)). Alternatively, can be set to NULL, which will typically render the map quicker but may cause countries far from the equator or large areas to appear distorted.

origin

Should the receptor point be marked with a circle? Defaults to TRUE.

map

Should a base map be drawn? Defaults to TRUE.

map.fill

Colour to use to fill the polygons of the base map (see colors()).

map.colour

Colour to use for the polygon borders of the base map (see colors()).

map.alpha

Transparency of the base map polygons. Must be between 0 (fully transparent) and 1 (fully opaque).

map.lwd

Line width of the base map polygon borders.

map.lty

Line type of the base map polygon borders. See ggplot2::scale_linetype() for common examples.

...

Arguments passed on to ggplot2::coord_sf

expand

If TRUE, the default, adds a small expansion factor to the limits to ensure that data and axes don't overlap. If FALSE, limits are taken exactly from the data or xlim/ylim.

datum

CRS that provides datum to use when generating graticules.

label_graticule

Character vector indicating which graticule lines should be labeled where. Meridians run north-south, and the letters "N" and "S" indicate that they should be labeled on their north or south end points, respectively. Parallels run east-west, and the letters "E" and "W" indicate that they should be labeled on their east or west end points, respectively. Thus, label_graticule = "SW" would label meridians at their south end and parallels at their west end, whereas label_graticule = "EW" would label parallels at both ends and meridians not at all. Because meridians and parallels can in general intersect with any side of the plot panel, for any choice of label_graticule labels are not guaranteed to reside on only one particular side of the plot panel. Also, label_graticule can cause labeling artifacts, in particular if a graticule line coincides with the edge of the plot panel. In such circumstances, label_axes will generally yield better results and should be used instead.

This parameter can be used alone or in combination with label_axes.

label_axes

Character vector or named list of character values specifying which graticule lines (meridians or parallels) should be labeled on which side of the plot. Meridians are indicated by "E" (for East) and parallels by "N" (for North). Default is "--EN", which specifies (clockwise from the top) no labels on the top, none on the right, meridians on the bottom, and parallels on the left. Alternatively, this setting could have been specified with list(bottom = "E", left = "N").

This parameter can be used alone or in combination with label_graticule.

lims_method

Method specifying how scale limits are converted into limits on the plot region. Has no effect when default_crs = NULL. For a very non-linear CRS (e.g., a perspective centered around the North pole), the available methods yield widely differing results, and you may want to try various options. Methods currently implemented include "cross" (the default), "box", "orthogonal", and "geometry_bbox". For method "cross", limits along one direction (e.g., longitude) are applied at the midpoint of the other direction (e.g., latitude). This method avoids excessively large limits for rotated coordinate systems but means that sometimes limits need to be expanded a little further if extreme data points are to be included in the final plot region. By contrast, for method "box", a box is generated out of the limits along both directions, and then limits in projected coordinates are chosen such that the entire box is visible. This method can yield plot regions that are too large. Finally, method "orthogonal" applies limits separately along each axis, and method "geometry_bbox" ignores all limit information except the bounding boxes of any objects in the geometry aesthetic.

ndiscr

Number of segments to use for discretising graticule lines; try increasing this number when graticules look incorrect.

default

Is this the default coordinate system? If FALSE (the default), then replacing this coordinate system with another one creates a message alerting the user that the coordinate system is being replaced. If TRUE, that warning is suppressed.

clip

Should drawing be clipped to the extent of the plot panel? A setting of "on" (the default) means yes, and a setting of "off" means no. In most cases, the default of "on" should not be changed, as setting clip = "off" can cause unexpected results. It allows drawing of data points anywhere on the plot, including in the plot margins. If limits are set via xlim and ylim and some data points fall outside those limits, then those data points may show up in places such as the axes, the legend, the plot title, or the plot margins.

Value

a ggplot2 plot

Examples

if (FALSE) {
# colour by height
trajMapStatic(traj_data) +
  ggplot2::scale_color_gradientn(colors = openair::openColours())

# colour by PM10, log transform scale
trajMapStatic(traj_data, colour = "pm10") +
  ggplot2::scale_color_viridis_c(trans = "log10") +
  ggplot2::labs(color = openair::quickText("PM10"))

# color by PM2.5, lat/lon projection
trajMapStatic(traj_data, colour = "pm2.5", crs = sf::st_crs(4326)) +
  ggplot2::scale_color_viridis_c(option = "turbo") +
  ggplot2::labs(color = openair::quickText("PM2.5"))
}

Trajectory line plots in `ggplot2`

Usage

Arguments

Value

See also

Examples