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Legend for color ramp maps

legend_ramp.Rd

This function plots a map legend that handles logarithmic scaling

Usage

legend_ramp(
  r,
  title,
  ColScheme,
  breaks,
  pos = c(0.2, 0.23, 0.1, 0.5),
  log = NULL,
  horizontal = FALSE,
  title.height = 1
)

Arguments

r

A spatial raster object, typically from the terra package.

title

Character. The title for the legend.

ColScheme

Character vector. Specifies the colors used for the legend. Typically corresponds to the color scheme applied to the raster data visualization.

breaks

Numeric vector. Defines the breakpoints for the legend, determining how the range of the raster is divided into intervals corresponding to the colors in ColScheme.

pos

Numeric vector of length 4. Defines the position of the legend as proportions of the raster extent. The format is c(xmin, xmax, ymin, ymax).

log

Numeric or NULL. The base of the logarithm used to compute legend labels. If NULL, values are displayed as-is.

horizontal

Logical. Should the legend be drawn horizontally? Default is FALSE.

title.height

Numeric. Scaling factor for the height of the legend title relative to the legend size.

Value

NULL. A plot of the legend is drawn in the current plotting device. The function does not return any value.

Details

The function uses the extent of the raster object to determine the positioning and size of the legend. The legend can be oriented either horizontally or vertically, and logarithmic scaling is applied to the labels if the log parameter is specified.

Examples

## get the sample digital elevation model (dem) provided with `climr`
dem <- get(data("dem_vancouver")) |> terra::unwrap()
## convert the DEM to a data.frame
grid <- as.data.frame(dem, cells = TRUE, xy = TRUE)
## rename column names to what climr expects
colnames(grid) <- c("id", "lon", "lat", "elev")
## A simple climr query.
## This will return the observed 1961-1990 normals for the raster grid points.
var <- "MAP"
ds_out <- downscale(grid, which_refmap = "refmap_climr", vars = var)
#> Welcome to climr!
#> Not fully cached :( Will download more
#> Downloading new data from refmap_climr...
#> .
#> Caching data...
#> Downscaling...
clim <- terra::rast(dem) # use the DEM as a template raster
## populate the raster cells with the 2001-2020 annual precipitation (MAP) values,
## using the `id` field as the link.
clim[ds_out[, id]] <- ds_out[, var, with = FALSE]
## log-transform precipitation for more meaningful scaling
clim <- log2(clim)
## increment for the ramp
inc=diff(range(terra::values(clim)))/500
## color breaks
breaks=seq(min(terra::values(clim))-inc, max(terra::values(clim))+inc, inc)
## color scheme
ColScheme <- rev(hcl.colors(length(breaks)-1, "GnBu"))
terra::plot(clim, col=ColScheme, breaks=breaks, legend=FALSE, main="", mar=NA)
legend_ramp(
  clim,
  title = paste(var, "(mm)"),
  ColScheme = ColScheme,
  breaks = breaks,
  pos=c(0.05, 0.45, 0.1, 0.125),
  log = 2,
  horizontal = TRUE
)