A surface and its uncertainty, interactively

The interactive counterpart of map_pair(): both quantities on one map, with a control to switch between them.

Usage

leaflet_pair(
  x,
  value,
  uncertainty,
  uncertainty_from = NULL,
  by = NULL,
  coords = NULL,
  crs = NULL,
  kind = c("surface", "probability"),
  uncertainty_kind = c("surface", "diverging"),
  uncertainty_midpoint = 0,
  uncertainty_direction = 1,
  labels = NULL,
  transform = "auto",
  limits = NULL,
  probs = c(0, 0.99),
  popup = NULL,
  tiles = "Esri.WorldGrayCanvas",
  opacity = 0.8,
  position = "topright"
)

Arguments

x: The geometry, or a map_data. Both panels are drawn from it unless uncertainty_from names a different object.
value: What the left panel colours by.
uncertainty: What the right panel colours by: a CV, a standard error, a posterior standard deviation, an extrapolation score.
uncertainty_from: A second object to take uncertainty from, when it does not live alongside value. Must cover the same cells.
by, coords, crs: Passed to as_map_data(). crs is also the CRS the map is drawn in – see display_crs() for what happens when it is not given.
kind: How the left panel is scaled: "surface" for a skewed positive quantity, "probability" for one bounded at 0 and 1.
uncertainty_kind: How the right panel is scaled. "surface" for a CV or an SE, which only increase; "diverging" for a signed score such as an extrapolation surface, which needs uncertainty_midpoint.
uncertainty_midpoint: The centre for a diverging right panel. Zero is the usual meaning and it is the default here, unlike in map_diverging(), because the caller has already said the panel is diverging.
uncertainty_direction: Which way the diverging ramp runs on the right panel. -1 puts the warm arm at the low end, which is what an extrapolation surface wants.
labels: A length-2 character vector naming the two quantities. These are what the switch is labelled with, so they should read as names rather than as units.
transform, limits, probs: Passed to surface_scale(), so the colours match the static map's exactly.
popup: Extra columns of x to show when a cell is clicked, as a character vector. The value and the join key are always shown. FALSE turns popups off.
tiles: A leaflet provider name for the basemap, or NULL for no basemap at all. The default is "Esri.WorldGrayCanvas", a quiet grey one, so the data is the brightest thing on the map rather than competing with a road network. It is also key-free: see the note on leaflet_base().
opacity: How opaque the cells are over the basemap.
position: Where the layer control sits.

Value

A leaflet widget.

Why one map and a switch, rather than two maps side by side

map_pair() draws two panels because a static figure has no other way to show two things at once, and it goes to some trouble – shared extent, shared projection, one coastline, aligned panels – to make them comparable cell by cell. All of that is machinery for approximating, on paper, something an interactive map gets for free.

Switching layers on one map is a blink comparison: the same cells, at the same position and the same zoom, changing only in the quantity drawn. Nothing has to be aligned because nothing moved. Two side-by-side widgets would reintroduce exactly the alignment problem map_pair() exists to solve, and would need a synchronisation dependency to solve it again.

The trade is that the two can no longer be seen simultaneously. When that is what you want – a figure for a manuscript, or a reader who cannot click – map_pair() is the one to use.

Each layer carries its own legend, shown and hidden with it, because the two are different quantities in different units.

Examples

if (FALSE) { # \dontrun{
grid <- example_grid()

leaflet_pair(grid, "density", "cv")

leaflet_pair(grid, "density", "mess", uncertainty_kind = "diverging",
             uncertainty_direction = -1,
             labels = c("density", "extrapolation"))
} # }

Usage

Arguments

Value

Why one map and a switch, rather than two maps side by side

See also

Examples