ms_simplify function

Topologically-aware geometry simplification.

Uses mapshaper to simplify polygons.

ms_simplify(
  input,
  keep = 0.05,
  method = NULL,
  weighting = 0.7,
  keep_shapes = FALSE,
  no_repair = FALSE,
  snap = TRUE,
  explode = FALSE,
  drop_null_geometries = TRUE,
  snap_interval = NULL,
  ...
)

Arguments

• input: spatial object to simplify. One of:

  • geo_json or character polygons or lines;
  • SpatialPolygons* or SpatialLines*;
  • sf or sfc polygons or lines object

• keep: proportion of points to retain (0-1; default 0.05)

• method: simplification method to use: "vis" for Visvalingam algorithm, or "dp" for Douglas-Peuker algorithm. If left as NULL (default), uses Visvalingam simplification but modifies the area metric by underweighting the effective area of points at the vertex of more acute angles, resulting in a smoother appearance. See this https://github.com/mbloch/mapshaper/wiki/Simplification-Tipslink

  for more information.

• weighting: Coefficient for weighting Visvalingam simplification (default is 0.7). Higher values produce smoother output. weighting=0 is equivalent to unweighted Visvalingam simplification.

• keep_shapes: Prevent small polygon features from disappearing at high simplification (default FALSE)

• no_repair: disable intersection repair after simplification (default FALSE).

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

• explode: Should multipart polygons be converted to singlepart polygons? This prevents small shapes from disappearing during simplification if keep_shapes = TRUE. Default FALSE

• drop_null_geometries: should Features with null geometries be dropped? Ignored for Spatial* objects, as it is always TRUE.

• snap_interval: Specify snapping distance in source units, must be a numeric. Default NULL

• ...: 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

a simplified representation of the geometry in the same class as the input

Examples

# With a simple geojson object
poly <- structure('{
 "type": "Feature",
 "properties": {},
 "geometry": {
   "type": "Polygon",
   "coordinates": [[
     [-70.603637, -33.399918],
     [-70.614624, -33.395332],
     [-70.639343, -33.392466],
     [-70.659942, -33.394759],
     [-70.683975, -33.404504],
     [-70.697021, -33.419406],
     [-70.701141, -33.434306],
     [-70.700454, -33.446339],
     [-70.694274, -33.458369],
     [-70.682601, -33.465816],
     [-70.668869, -33.472117],
     [-70.646209, -33.473835],
     [-70.624923, -33.472117],
     [-70.609817, -33.468107],
     [-70.595397, -33.458369],
     [-70.587158, -33.442901],
     [-70.587158, -33.426283],
     [-70.590591, -33.414248],
     [-70.594711, -33.406224],
     [-70.603637, -33.399918]
   ]]
 }
}', class = c("geojson", "json"))

ms_simplify(poly, keep = 0.1)

# With an sf object

poly_sf <- geojsonsf::geojson_sf(poly)
ms_simplify(poly_sf, keep = 0.5)