ms_dissolve function

Aggregate shapes in a polygon or point layer.

Aggregates using specified field, or all shapes if no field is given. For point layers, replaces a group of points with their centroid.

ms_dissolve(
  input,
  field = NULL,
  sum_fields = NULL,
  copy_fields = NULL,
  weight = NULL,
  snap = TRUE,
  ...
)

Arguments

• input: spatial object to dissolve. One of:

  • geo_json or character points or polygons;
  • SpatialPolygons, or SpatialPoints

• field: the field to dissolve on

• sum_fields: fields to sum

• copy_fields: fields to copy. The first instance of each field will be copied to the aggregated feature.

• weight: Name of an attribute field for generating weighted centroids (points only).

• snap: Snap together vertices within a small distance threshold to fix small coordinate misalignment in adjacent polygons. Default TRUE.

• ...: Arguments passed on to apply_mapshaper_commands

  • force_FC: should the output be forced to be a FeatureCollection (or sf object or Spatial*DataFrame) even if there are no attributes? Default TRUE. If FALSE and there are no attributes associated with the geometries, a GeometryCollection (or Spatial object with no dataframe, or sfc) will be output.
  • sys: Should the system mapshaper be used instead of the bundled mapshaper? Gives better performance on large files. Requires the mapshaper node package to be installed and on the PATH.
  • sys_mem: How much memory (in GB) should be allocated if using the system mapshaper (sys = TRUE)? Default 8. Ignored if sys = FALSE. This can also be set globally with the option "mapshaper.sys_mem"
  • quiet: If sys = TRUE, should the mapshaper messages be silenced? Default FALSE. This can also be set globally with the option "mapshaper.sys_quiet"

Returns

the same class as the input

Examples

library(geojsonsf)
library(sf)

poly <- structure('{"type":"FeatureCollection",
  "features":[
  {"type":"Feature",
  "properties":{"a": 1, "b": 2},
  "geometry":{"type":"Polygon","coordinates":[[
  [102,2],[102,3],[103,3],[103,2],[102,2]
  ]]}}
  ,{"type":"Feature",
  "properties":{"a": 5, "b": 3},
  "geometry":{"type":"Polygon","coordinates":[[
  [100,0],[100,1],[101,1],[101,0],[100,0]
  ]]}}]}', class = c("geojson", "json"))
poly <- geojson_sf(poly)
plot(poly)
length(poly)
poly

# Dissolve the polygon
out <- ms_dissolve(poly)
plot(out)
length(out)
out

# Dissolve and summing columns
out <- ms_dissolve(poly, sum_fields = c("a", "b"))
plot(out)
out