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Prop Type: Scale

Source: R/doc-proptypes.R
scale.Rd

Scales transform input data into visual representations, predominantly:

  • colours: fill, line, highlight

  • sizes: radius, elevation, width, height

Transformations are performed in client-side javascript, thus scales have very minimal file-size overhead; what you pay for is the source data being scaled & the scale descriptor (palette, breaks, etc), but you don't pay for the scaled output (e.g. the vector of colours). Many scales can refer to the same column of a dataframe, but the column will only be serialised once.

Data retrieved in the browser dynamically can also be scaled, including mvt_layer(). All rdeck scales (except scale_quantile()) support both R dataframes and data fetched in javascript, with the following restrictions:

  • column validation isn't performed – missing column / incorrect type may error in javascript, or result in the na_color / na_value used for all features

  • limits / levels must be explictly defined in the scale – they cannot be learnt from data

  • quantile scales technically work, but they require a copy of the data to compute the quantiles

Tidy-eval

Columns referenced by a scale support tidy-eval expressions. The col parameter for a scale must be a valid argument to rlang::ensym() and follows the same rules. Use the injection operators to pass the value of a name from the environment, e.g. !!my_column.

Legend

Scales can optionally produce a colour or numeric legend in the client. Numeric legends give context for which visual field is being scaled and by what column; colour legends additionally provide a colour scale and untransformed ticks.

Legend ticks can be formatted with a labelling function (e.g. scales::label_number()). This function can completely replace the input ticks if you wish; the only constraint is the return value is a character vector of the same length as input unformatted ticks.

Legends are kepler.gl inspired.

Available scales