compare function

Create a Compare widget

This function creates a comparison view between two Mapbox GL or Maplibre GL maps, allowing users to either swipe between the two maps or view them side-by-side with synchronized navigation.

compare(
  map1,
  map2,
  width = "100%",
  height = NULL,
  elementId = NULL,
  mousemove = FALSE,
  orientation = "vertical",
  mode = "swipe"
)

Arguments

• map1: A mapboxgl or maplibre object representing the first map.
• map2: A mapboxgl or maplibre object representing the second map.
• width: Width of the map container.
• height: Height of the map container.
• elementId: An optional string specifying the ID of the container for the comparison. If NULL, a unique ID will be generated.
• mousemove: A logical value indicating whether to enable swiping during cursor movement (rather than only when clicked). Only applicable when mode="swipe".
• orientation: A string specifying the orientation of the swiper or the side-by-side layout, either "horizontal" or "vertical".
• mode: A string specifying the comparison mode: "swipe" (default) for a swipeable comparison with a slider, or "sync" for synchronized maps displayed next to each other.

Returns

A comparison widget.

Details

Comparison modes

The compare() function supports two modes:

• mode="swipe" (default) - Creates a swipeable interface with a slider to reveal portions of each map
• mode="sync" - Places the maps next to each other with synchronized navigation

In both modes, navigation (panning, zooming, rotating, tilting) is synchronized between the maps.

Using the compare widget in Shiny

The compare widget can be used in Shiny applications with the following functions:

• mapboxglCompareOutput() / renderMapboxglCompare() - For Mapbox GL comparisons
• maplibreCompareOutput() / renderMaplibreCompare() - For Maplibre GL comparisons
• mapboxgl_compare_proxy() / maplibre_compare_proxy() - For updating maps in a compare widget

After creating a compare widget in a Shiny app, you can use the proxy functions to update either the "before" (left/top) or "after" (right/bottom) map. The proxy objects work with all the regular map update functions like set_style(), set_paint_property(), etc.

To get a proxy that targets a specific map in the comparison:

# Access the left/top map
left_proxy <- maplibre_compare_proxy("compare_id", map_side = "before")

# Access the right/bottom map
right_proxy <- maplibre_compare_proxy("compare_id", map_side = "after")

The compare widget also provides Shiny input values for view state and clicks. For a compare widget with ID "mycompare", you'll have:

• input$mycompare_before_view - View state (center, zoom, bearing, pitch) of the left/top map
• input$mycompare_after_view - View state of the right/bottom map
• input$mycompare_before_click - Click events on the left/top map
• input$mycompare_after_click - Click events on the right/bottom map

Examples

## Not run:

library(mapgl)

m1 <- mapboxgl(style = mapbox_style("light"))
m2 <- mapboxgl(style = mapbox_style("dark"))

# Default swipe mode
compare(m1, m2)

# Synchronized side-by-side mode
compare(m1, m2, mode = "sync")

# Shiny example
library(shiny)

ui <- fluidPage(
  maplibreCompareOutput("comparison")
)

server <- function(input, output, session) {
  output$comparison <- renderMaplibreCompare({
    compare(
      maplibre(style = carto_style("positron")),
      maplibre(style = carto_style("dark-matter")),
      mode = "sync"
    )
  })

  # Update the right map
  observe({
    right_proxy <- maplibre_compare_proxy("comparison", map_side = "after")
    set_style(right_proxy, carto_style("voyager"))
  })
}
## End(Not run)