# NOT RUN {
library(ggplot2)
g <- ggplot(seals, aes(long, lat)) +
geom_vector(aes(dx = delta_long, dy = delta_lat), skip = 2)
g + scale_mag("Seals velocity")
g + scale_mag("Seals velocity", max = 1)
g + scale_mag("Seals velocity", max_size = 2)
g + scale_mag("Seals velocity", default_unit = "mm")
# }
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