Suggest automatic region offsets for a draggable map

Computes a starting layout for drag_map_prototype() or render_dragged_map() without manual dragging. The result is a data frame of offsets that can be refined interactively in the browser.

Usage

suggest_offsets(
  x,
  region_col,
  method = c("radial", "horizontal", "vertical", "grid", "none"),
  scale = 1
)

Arguments

x

An sf object in a projected CRS.

region_col

Column in x defining draggable groups.

method

Layout algorithm. One of "radial" (default), "horizontal", "vertical", "grid", or "none".

scale

Positive numeric multiplier applied to all offsets. Defaults to 1. Values greater than 1 push regions further apart.

Value

A data frame with region, dx_m, and dy_m columns, one row per unique region value. Suitable for use as region_offsets in drag_map_prototype() or render_dragged_map().

Details

Available layout methods:

"radial"

Each region is pushed outward from the collective centroid in the direction of its own centroid. Regions that are already spread out are pushed further than regions near the centre.

"horizontal"

Regions are ranked by centroid x-coordinate and spread evenly along the x-axis. Useful for left-to-right layouts.

"vertical"

Regions are ranked by centroid y-coordinate and spread evenly along the y-axis.

"grid"

Regions are arranged in a rectangular grid ordered by centroid position (top-to-bottom, left-to-right).

"none"

Returns zero offsets for every region. Useful as a placeholder when you want to start from an undisplaced state.

The scale argument multiplies all computed offsets uniformly. Increase it to spread regions further apart; decrease it for a tighter layout.

See also

drag_map_prototype() to open the interactive helper with the suggested layout as a starting point; apply_offsets() to apply offsets directly to an sf object.

Examples

poly <- sf::st_sf(
  region = c("A", "B", "C", "D"),
  geometry = sf::st_sfc(
    sf::st_polygon(list(rbind(c(0,1e5),c(1e5,1e5),c(1e5,2e5),c(0,2e5),c(0,1e5)))),
    sf::st_polygon(list(rbind(c(0,0),c(1e5,0),c(1e5,1e5),c(0,1e5),c(0,0)))),
    sf::st_polygon(list(rbind(c(1e5,1e5),c(2e5,1e5),c(2e5,2e5),c(1e5,2e5),c(1e5,1e5)))),
    sf::st_polygon(list(rbind(c(1e5,0),c(2e5,0),c(2e5,1e5),c(1e5,1e5),c(1e5,0)))),
    crs = 3857
  )
)
suggest_offsets(poly, region_col = "region", method = "radial")
#>   region      dx_m      dy_m
#> 1      A -34641.02  34641.02
#> 2      B -34641.02 -34641.02
#> 3      C  34641.02  34641.02
#> 4      D  34641.02 -34641.02
suggest_offsets(poly, region_col = "region", method = "horizontal")
#>   region      dx_m dy_m
#> 1      A -73484.69    0
#> 2      B -24494.90    0
#> 3      C  24494.90    0
#> 4      D  73484.69    0
suggest_offsets(poly, region_col = "region", method = "grid")
#>   region      dx_m      dy_m
#> 1      A -48989.79  48989.79
#> 2      B -48989.79 -48989.79
#> 3      C  48989.79  48989.79
#> 4      D  48989.79 -48989.79