ms_filter_islands: Remove small detached polygons (islands)
In rmapshaper: Edit 'GeoJSON' and Spatial Objects

Description Usage Arguments Value Examples

View source: R/filter_islands.R

Remove small detached polygons, keeping those with a minimum area and/or a minimum number of vertices. Optionally remove null geomtries.

1 2	ms_filter_islands(input, min_area = NULL, min_vertices = NULL, drop_null_geometries = TRUE, force_FC = TRUE)

`input`	spatial object to filter. One of: `geo_json` or `character` polygons; `geo_list` polygons; `SpatialPolygons*`
`min_area`	minimum area of polygons to retain. Area is calculated using planar geometry, except for the area of unprojected polygons, which is calculated using spherical geometry in units of square meters.
`min_vertices`	minimum number of vertices in polygons to retain.
`drop_null_geometries`	should features with empty geometries be dropped? Default `TRUE`. Ignored for `SpatialPolyons*`, as it is always `TRUE`.
`force_FC`	should the output be forced to be a `FeatureCollection` even if there are no attributes? Default `TRUE`. `FeatureCollections` are more compatible with `rgdal::readOGR` and `geojsonio::geojson_sp`. If `FALSE` and there are no attributes associated with the geometries, a `GeometryCollection` will be output. Ignored for `Spatial` objects, as the output is always the same class as the input.

object with only specified features retained, in the same class as the input

library(geojsonio)
library(sp)

poly <- structure("{\"type\":\"FeatureCollection\",
           \"features\":[{\"type\":\"Feature\",\"properties\":{},
           \"geometry\":{\"type\":\"Polygon\",
           \"coordinates\":[[[102,2],[102,4],[104,4],[104,2],[102,2]]]}},
           {\"type\":\"Feature\",\"properties\":{},
           \"geometry\":{\"type\":\"Polygon\",
           \"coordinates\":[[[100,2],[98,4],[101.5,4],[100,2]]]}},
           {\"type\":\"Feature\",\"properties\":{},
           \"geometry\":{\"type\":\"Polygon\",
           \"coordinates\":[[[100,0],[100,1],[101,1],[101,0],[100,0]]]}}]}",
           class = c("json", "geo_json"))

poly <- geojson_sp(poly)
plot(poly)

out <- ms_filter_islands(poly, min_area = 12391399903)
plot(out)