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Write TopoJSON from various inputs

Source: R/topojson_write.R
topojson_write.Rd

Write TopoJSON from various inputs

Usage

topojson_write(
  input,
  lat = NULL,
  lon = NULL,
  geometry = "point",
  group = NULL,
  file = "myfile.topojson",
  overwrite = TRUE,
  precision = NULL,
  convert_wgs84 = FALSE,
  crs = NULL,
  object_name = "foo",
  quantization = 0,
  ...
)

Arguments

input

Input list, data.frame, spatial class, or sf class. Inputs can also be dplyr tbl_df class since it inherits from data.frame

lat

(character) Latitude name. The default is NULL, and we attempt to guess.

lon

(character) Longitude name. The default is NULL, and we attempt to guess.

geometry

(character) One of point (Default) or polygon.

group

(character) A grouping variable to perform grouping for polygons - doesn't apply for points

file

(character) A path and file name (e.g., myfile), with the .geojson file extension. Default writes to current working directory.

overwrite

(logical) Overwrite the file given in file with input. Default: TRUE. If this param is FALSE and the file already exists, we stop with error message.

precision

desired number of decimal places for the coordinates in the geojson file. Using fewer decimal places can decrease file sizes (at the cost of precision).

convert_wgs84

Should the input be converted to the standard CRS for GeoJSON (https://tools.ietf.org/html/rfc7946) (geographic coordinate reference system, using the WGS84 datum, with longitude and latitude units of decimal degrees; EPSG: 4326). Default is FALSE though this may change in a future package version. This will only work for sf or Spatial objects with a CRS already defined. If one is not defined but you know what it is, you may define it in the crs argument below.

crs

The CRS of the input if it is not already defined. This can be an epsg code as a four or five digit integer or a valid proj4 string. This argument will be ignored if convert_wgs84 is FALSE or the object already has a CRS.

object_name

(character) name to give to the TopoJSON object created. Default: "foo"

quantization

(numeric) quantization parameter, use this to quantize geometry prior to computing topology. Typical values are powers of ten (1e4, 1e5, ...), default is 0 to not perform quantization. For more information about quantization, see this by Mike Bostock https://stackoverflow.com/questions/18900022/topojson-quantization-vs-simplification/18921214#18921214

...

Further args passed on to internal functions. For Spatial* classes, data.frames, regular lists, and numerics, it is passed through to sf::st_write(). For sf classes, geo_lists and json classes, it is passed through to jsonlite::toJSON().

Value

A topojson_write class, with two elements:

  • path: path to the file with the TopoJSON

  • type: type of object the TopoJSON came from, e.g., SpatialPoints

Details

Under the hood we simply wrap geojson_write(), then take the GeoJSON output of that operation, then convert to TopoJSON with geo2topo(), then write to disk.

Unfortunately, this process requires a number of round trips to disk, so speed ups will hopefully come soon.

Any intermediate geojson files are cleaned up (deleted).

See also

geojson_write(), topojson_read()