Aggregate shapes in a polygon or point layer. — ms

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

Usage

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"
gj2008: Generate output that is consistent with the pre-RFC 7946 GeoJSON spec (dating to 2008). Polygon rings are CW and holes are CCW, which is the opposite of the default RFC 7946-compatible output. This should be rarely needed, though may be useful when preparing data for D3-based data visualizations (such as plotly::plot_ly()). Default FALSE

Value

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)
#> [1] 3
poly
#> Simple feature collection with 2 features and 2 fields
#> Geometry type: POLYGON
#> Dimension:     XY
#> Bounding box:  xmin: 100 ymin: 0 xmax: 103 ymax: 3
#> Geodetic CRS:  WGS 84
#>   a b                       geometry
#> 1 1 2 POLYGON ((102 2, 102 3, 103...
#> 2 5 3 POLYGON ((100 0, 100 1, 101...

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

length(out)
#> [1] 1
out
#> Simple feature collection with 1 feature and 0 fields
#> Geometry type: MULTIPOLYGON
#> Dimension:     XY
#> Bounding box:  xmin: 100 ymin: 0 xmax: 103 ymax: 3
#> Geodetic CRS:  WGS 84
#>                         geometry
#> 1 MULTIPOLYGON (((102 2, 103 ...

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

out
#> Simple feature collection with 1 feature and 2 fields
#> Geometry type: MULTIPOLYGON
#> Dimension:     XY
#> Bounding box:  xmin: 100 ymin: 0 xmax: 103 ymax: 3
#> Geodetic CRS:  WGS 84
#>   a b                       geometry
#> 1 6 5 MULTIPOLYGON (((102 2, 103 ...