Export an exploded map as TopoJSON

Converts an sf, exploded_map, or grouped_exploded_map object to TopoJSON using the external mapshaper command-line tool. The input is first written as a temporary GeoJSON file, then converted by mapshaper.

Usage

export_topojson(x, file, simplify = NULL, overwrite = FALSE)

Arguments

x

An sf, exploded_map, or grouped_exploded_map object. For exploded_map objects, the WGS84 exploded geometry (sf_exp_wgs) is exported. For grouped_exploded_map objects, the WGS84 grouped geometry (sf_grouped_wgs) is exported.

file

Output file path. Should end in .topojson or .json.

simplify

Optional simplification proportion passed to mapshaper -simplify. Must be a single number between 0 and 1 (exclusive). For example, simplify = 0.5 retains 50% of vertices. Default is NULL (no simplification). Note that simplification modifies polygon geometry and therefore breaks the exact geometry preservation guarantee of Proposition 1.

overwrite

Logical; if TRUE, overwrite file if it already exists. Default is FALSE.

Value

Invisibly returns the output file path.

Details

This is intended as a convenience helper for downstream tools such as Power BI, D3.js, and Observable that prefer or require TopoJSON input.

This function requires the external mapshaper command-line tool to be installed and available on the system path. It can be installed with:

npm install -g mapshaper

The mapshaper tool is not an R package dependency; it is invoked via system2(). If mapshaper is not found, the function errors with an informative message.

Examples

if (FALSE) { # \dontrun{
# Two-level export
result <- explode_sf(my_sf, region_col = "region", plot = FALSE)
export_topojson(result, "exploded.topojson")

# Three-level grouped export
grp <- explode_grouped(my_sf, region_col = "region", plot = FALSE)
export_topojson(grp, "grouped.topojson")

# With simplification (breaks Proposition 1 guarantee)
export_topojson(result, "simplified.topojson", simplify = 0.5)

# Raw sf object
export_topojson(my_sf, "raw.topojson", overwrite = TRUE)
} # }