Data frame, the result of importing a trajectory file using importTraj.

Column containing the longitude, as a decimal.

Column containing the latitude, as a decimal.

Pollutant to be plotted. By default the trajectory height is used.

type determines how the data are split i.e. conditioned, and then plotted. The default is will produce a single plot using the entire data. Type can be one of the built-in types as detailed in cutData e.g. "season", "year", "weekday" and so on. For example, type = "season" will produce four plots — one for each season.

It is also possible to choose type as another variable in the data frame. If that variable is numeric, then the data will be split into four quantiles (if possible) and labelled accordingly. If type is an existing character or factor variable, then those categories/levels will be used directly. This offers great flexibility for understanding the variation of different variables and how they depend on one another.

type can be up length two e.g. type = c("season", "weekday") will produce a 2x2 plot split by season and day of the week. Note, when two types are provided the first forms the columns and the second the rows.

Should a base map be drawn? If TRUE the world base map from the maps package is used.

It is sometimes useful to group and colour trajectories according to a grouping variable. See example below.

Should the base map be a filled polygon? Default is to fill countries.

The resolution of the base map. By default the function uses the ‘world’ map from the maps package. If map.res = "hires" then the (much) more detailed base map ‘worldHires’ from the mapdata package is used. Use library(mapdata). Also available is a map showing the US states. In this case map.res = "state" should be used.

If map.fill = TRUE map.cols controls the fill colour. Examples include map.fill = "grey40" and map.fill = openColours("default", 10). The latter colours the countries and can help differentiate them.

The transpency level of the filled map which takes values from 0 (full transparency) to 1 (full opacity). Setting it below 1 can help view trajectories, trajectory surfaces etc. and a filled base map.

The map projection to be used. Different map projections are possible through the mapproj package. See ?mapproject for extensive details and information on setting other parameters and orientation (see below).

From the mapproj package. Optional numeric vector of parameters for use with the projection argument. This argument is optional only in the sense that certain projections do not require additional parameters. If a projection does not require additional parameters then set to null i.e. parameters = NULL.

From the mapproj package. An optional vector c(latitude, longitude, rotation) which describes where the "North Pole" should be when computing the projection. Normally this is c(90, 0), which is appropriate for cylindrical and conic projections. For a planar projection, you should set it to the desired point of tangency. The third value is a clockwise rotation (in degrees), which defaults to the midrange of the longitude coordinates in the map.

The colour of the map grid to be used. To remove the grid set grid.col = "transparent".

A dot is placed every npoints along each full trajectory. For hourly back trajectories points are plotted every npoint 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 togther correspond to slower moving air masses). If npoints = NA then no points are added.

If true a filled circle dot is shown to mark the receptor point.

other arguments are passed to cutData and scatterPlot. This provides access to arguments used in both these functions and functions that they in turn pass arguments on to. For example, plotTraj passes the argument cex on to scatterPlot which in turn passes it on to the lattice function xyplot where it is applied to set the plot symbol size.