# Convert many input types with spatial data to TopoJSON as a JSON string ```r topojson_json( input, lat = NULL, lon = NULL, group = NULL, geometry = "point", type = "FeatureCollection", 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. - `group`: (character) A grouping variable to perform grouping for polygons - doesn't apply for points - `geometry`: (character) One of point (Default) or polygon. - `type`: (character) The type of collection. One of 'auto' (default for 'sf' objects), 'FeatureCollection' (default for everything else), or 'GeometryCollection'. "skip" skips the coercion with package `geojson` functions; skipping can save significant run time on larger geojson objects. `Spatial` objects can only accept "FeatureCollection" or "skip". "skip" is not available as an option for `numeric`, `list`, and `data.frame` classes - `convert_wgs84`: Should the input be converted to the standard CRS system 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 - `...`: args passed down to `geojson_json()`; see `geojson_json()` for help on what's supported here ## Returns An object of class `geo_json` (and `json`) ## Details The `type` parameter is automatically converted to `type="auto"` if a sf, sfc, or sfg class is passed to `input` ## Examples ```r ## Not run: # From a numeric vector of length 2, making a point type topojson_json(c(-99.74, 32.45), pretty = TRUE) topojson_json(c(-99.74, 32.45), type = "GeometryCollection") ## polygon type ### this requires numeric class input, so inputting a list will dispatch on the list method poly <- c( c(-114.345703125, 39.436192999314095), c(-114.345703125, 43.45291889355468), c(-106.61132812499999, 43.45291889355468), c(-106.61132812499999, 39.436192999314095), c(-114.345703125, 39.436192999314095) ) topojson_json(poly, geometry = "polygon", pretty = TRUE) # Lists ## From a list of numeric vectors to a polygon vecs <- list(c(100.0, 0.0), c(101.0, 0.0), c(101.0, 1.0), c(100.0, 1.0), c(100.0, 0.0)) topojson_json(vecs, geometry = "polygon", pretty = TRUE) ## from a named list mylist <- list( list(latitude = 30, longitude = 120, marker = "red"), list(latitude = 30, longitude = 130, marker = "blue") ) topojson_json(mylist, lat = "latitude", lon = "longitude") # From a data.frame to points topojson_json(us_cities[1:2, ], lat = "lat", lon = "long", pretty = TRUE) topojson_json(us_cities[1:2, ], lat = "lat", lon = "long", type = "GeometryCollection", pretty = TRUE ) # from data.frame to polygons head(states) ## make list for input to e.g., rMaps topojson_json(states[1:351, ], lat = "lat", lon = "long", geometry = "polygon", group = "group") # from a geo_list a <- geojson_list(us_cities[1:2, ], lat = "lat", lon = "long") topojson_json(a) # sp classes ## From SpatialPolygons class library("sp") poly1 <- Polygons(list(Polygon(cbind( c(-100, -90, -85, -100), c(40, 50, 45, 40) ))), "1") poly2 <- Polygons(list(Polygon(cbind( c(-90, -80, -75, -90), c(30, 40, 35, 30) ))), "2") sp_poly <- SpatialPolygons(list(poly1, poly2), 1:2) topojson_json(sp_poly) topojson_json(sp_poly, pretty = TRUE) ## data.frame to geojson geojson_write(us_cities[1:2, ], lat = "lat", lon = "long") %>% as.json() # From SpatialPoints class x <- c(1, 2, 3, 4, 5) y <- c(3, 2, 5, 1, 4) s <- SpatialPoints(cbind(x, y)) topojson_json(s) ## From SpatialPointsDataFrame class s <- SpatialPointsDataFrame(cbind(x, y), mtcars[1:5, ]) topojson_json(s) ## From SpatialLines class library("sp") c1 <- cbind(c(1, 2, 3), c(3, 2, 2)) c2 <- cbind(c1[, 1] + .05, c1[, 2] + .05) c3 <- cbind(c(1, 2, 3), c(1, 1.5, 1)) L1 <- Line(c1) L2 <- Line(c2) L3 <- Line(c3) Ls1 <- Lines(list(L1), ID = "a") Ls2 <- Lines(list(L2, L3), ID = "b") sl1 <- SpatialLines(list(Ls1)) sl12 <- SpatialLines(list(Ls1, Ls2)) topojson_json(sl1) topojson_json(sl12) ## From SpatialLinesDataFrame class dat <- data.frame( X = c("Blue", "Green"), Y = c("Train", "Plane"), Z = c("Road", "River"), row.names = c("a", "b") ) sldf <- SpatialLinesDataFrame(sl12, dat) topojson_json(sldf) topojson_json(sldf, pretty = TRUE) ## From SpatialGrid x <- GridTopology(c(0, 0), c(1, 1), c(5, 5)) y <- SpatialGrid(x) topojson_json(y) ## From SpatialGridDataFrame sgdim <- c(3, 4) sg <- SpatialGrid(GridTopology(rep(0, 2), rep(10, 2), sgdim)) sgdf <- SpatialGridDataFrame(sg, data.frame(val = 1:12)) topojson_json(sgdf) # From SpatialPixels library("sp") pixels <- suppressWarnings(SpatialPixels(SpatialPoints(us_cities[c("long", "lat")]))) summary(pixels) topojson_json(pixels) # From SpatialPixelsDataFrame library("sp") pixelsdf <- suppressWarnings( SpatialPixelsDataFrame(points = canada_cities[c("long", "lat")], data = canada_cities) ) topojson_json(pixelsdf) # From sf classes: if (require(sf)) { ## sfg (a single simple features geometry) p1 <- rbind(c(0, 0), c(1, 0), c(3, 2), c(2, 4), c(1, 4), c(0, 0)) poly <- rbind(c(1, 1), c(1, 2), c(2, 2), c(1, 1)) poly_sfg <- st_polygon(list(p1)) topojson_json(poly_sfg) ## sfc (a collection of geometries) p1 <- rbind(c(0, 0), c(1, 0), c(3, 2), c(2, 4), c(1, 4), c(0, 0)) p2 <- rbind(c(5, 5), c(5, 6), c(4, 5), c(5, 5)) poly_sfc <- st_sfc(st_polygon(list(p1)), st_polygon(list(p2))) topojson_json(poly_sfc) ## sf (collection of geometries with attributes) p1 <- rbind(c(0, 0), c(1, 0), c(3, 2), c(2, 4), c(1, 4), c(0, 0)) p2 <- rbind(c(5, 5), c(5, 6), c(4, 5), c(5, 5)) poly_sfc <- st_sfc(st_polygon(list(p1)), st_polygon(list(p2))) poly_sf <- st_sf(foo = c("a", "b"), bar = 1:2, poly_sfc) topojson_json(poly_sf) } ## Pretty print a json string topojson_json(c(-99.74, 32.45)) topojson_json(c(-99.74, 32.45)) %>% pretty() ## End(Not run) ```

topojson_json function