Use mapview r package to display vector data with outline only

Question

I'm creating a map in r using the mapview package. I have a raster layer with a vector layer displayed over it. I want to view the raster data completely. How do you set vector data to be completely transparent (i.e. just an outline)?

A reproducible example from their vignette:

m1 <- mapView(franconia, col.regions = "red")
m2 <- mapView(breweries)
### add two mapview objects
m1 + m2
'+'(m2, m1)
### add layers to a mapview object
if (interactive()) {
library(plainview)
m1 + breweries + plainview::poppendorf[[4]]
}

In this example, I would want breweries to be completely transparent. However changing col.regions = 'transparent' for breweries isn't what I'm looking for. It's still opaque as seen when clicking on the zoom button (plainview::poppendorf[[4]]) on the lower right hand side.

Answer 1

alpha.regions parameter is the answer:

m1 <- mapview::mapview(ndvi_cropped_20181005, map.types = 'OpenStreetMap')
m2 <- mapview::mapview(fallowed_reprojected, color = 'cyan', alpha.regions = 0)
m1 + m2