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General function for producing scale keys for other openair functions. The function is a crude modification of the draw.colorkey function developed by Deepayan Sarkar as part of the lattice package, and allows additional key labelling to added, and provides some additional control of the appearance and scaling.


drawOpenKey(key, draw = FALSE, vp = NULL)



List defining the scale key structure to be produced. Most options are identical to original draw.colorkey function.

Original draw.colorkey options:

space location of the scale key ("left", "right", "top" or "bottom"). Defaults to "right".

col vector of colours, used in scale key.

at numeric vector specifying where the colors change. Must be of length 1 more than the col vector.

labels a character vector for labelling the at values, or more commonly, a list describing characteristics of the labels. This list may include components labels, at, cex, col, rot, font, fontface and fontfamily.

tick.number approximate number of ticks.

width width of the key.

height height of key.

Note: width and height refer to the key dimensions. height is the length of the key along the plot axis it is positioned against, and width is the length perpendicular to that.

Additional options include:

header a character vector of extra text to be added above the key, or a list describing some characteristics of the header. This list may include components header, the character vector of header labels, tweaks, a list of local controls, e.g. 'gap' and 'balance' for spacing relative to scale and footer, respectively, auto.text, TRUE/FALSE option to apply quickText, and slot, a numeric vector setting the size of the text boxes header text is placed in.

footer as in header but for labels below the scale key.

Notes: header and footer formatting can not be set locally, but instead are matched to those set in labels. drawOpenKey allows for up to six additional labels (three above and three below scale key). Any additional text is ignored.

tweak, auto.text, slot as in header and footer but sets all options uniformly. This also overwrites anything in header and/or footer.

fit the fit method to be applied to the header, scale key and footer when placing the scale key left or right of the plot. Options include: 'all', 'soft' and 'scale'. The default 'all' fits header, key and footer into height range. The alternative 'scale' fits only the key within height. (This means that keys keep the same proportions relative to the main plot regardless of positioning but that header and footer may exceed plot dimensions if height and/or slots are too large. a character vector of key plotting style instructions: Options currently include: 'paddle', 'ticks' and 'border'. 'paddle' applies the incremental paddle layout used by winRose. 'ticks' places ticks between the labels scale key. 'border' places a border about the scale key. Any combination of these may be used but if none set, scale key defaults to c("ticks", "border") for most plotting operations or c("paddle") for windRose.


Option to return the key object or plot it directly. The default, FALSE, should always be used within openair calls.


View port to be used when plotting key. The default, NULL, should always be used within openair calls.

(Note: drawOpenKey is a crude modification of lattice::draw.colorkey, that provides labelling options for openair plot scale keys. Some aspects of the function are in development and may to subject to change. Therefore, it is recommended that you use parent openair function controls, e.g. key.position, key.header, key.footer options, where possible. drawOpenKey may obviously be used in other plots but it is recommended that draw.colorkey itself be used wherever this type of additional scale labelling is not required.)


The function is a modification of lattice::draw.colorkey and returns a scale key using a similar mechanism to that used in in the original function as developed by Deepayan Sarkar.


The drawOpenKey function produces scale keys for other openair functions.

Most drawOpenKey options are identical to those of lattice::draw.colorkey. For example, scale key size and position are controlled via height, width and space. Likewise, the axis labelling can be set in and formatted by labels. See draw.colorkey for further details.

Additional scale labelling may be added above and below the scale using header and footer options within key. As in other openair functions, automatic text formatting can be enabled via auto.key.

(Note: Currently, the formatting of header and footer text are fixed to the same style as labels (the scale axis) and cannot be defined locally.)

The relationship between header, footer and the scale key itself can be controlled using fit options. These can be set in key$fit to apply uniform control or individually in key$header$fit and/or key$footer$fit to control locally.

The appearance of the scale can be controlled using


We gratefully acknowledge the considerable help and advice of Deepayan Sarkar.


Deepayan Sarkar (2010). lattice: Lattice Graphics. R package version 0.18-5.

See also

Functions using drawOpenKey currently include windRose, pollutionRose.

For details of the original function, see draw.colorkey


draw.colorkey is part of the lattice package, developed by Deepayan Sarkar.

Additional modifications by Karl Ropkins.


#example 1

#paddle style scale key used by windRose


#adding text and changing style and position via key

#some simple key control also possible directly
#For example, below does same as
#windRose(mydata, key.position="right")

   key =list(space="right")

#more detailed control possible working with
#key and drawOpenKey. For example,

   key = list(header="Title", footer="wind speed",
     = c("ticks", "border"),
              fit = "all", height = 1,
              space = "top")