Do you know the interrupted Goode homolosine projection? - What would happen if we peeled the Earth like an orange? The interrupted Goode homolosine projection gives us something close to that! This e...

I often need to get mainland from country / administrative region polygons, so I finally decided to write a function to help automate it. It selects the N largest feature(s) in a polygons or lines map. Here’s the code: selectLargest <- function(x, # terra SpatVector polygons or lines n = 1, # number of largest features to retain dissolve = FALSE, # whether to group contiguous features singleparts = TRUE # whether to disaggregate multi-part features ) { stopifnot(inherits(x, "SpatVector"), terra::geomtype(x) %in% c("polygons", "lines")) if (dissolve) { x <- terra::aggregate(x) } if (singleparts) { x <- terra::disagg(x) } if (terra::is.polygons(x)) { size_rank <- order(terra::expanse(x), decreasing = TRUE) } else if (terra::is.lines(x)) { size_rank <- order(terra::perim(x), decreasing = TRUE) } x[size_rank[1:n], ] } The dissolving of internal borders is optional. Here are some usage examples: # import a USA map and get the conterminous and continental parts: usa <- geodata::gadm("United States", level = 1, path = tempdir()) mainland_usa <- selectLargest(usa, dissolve = TRUE) contin_usa <- selectLargest(usa, dissolve = TRUE, n = 2) # two largest polygons, to include Alaska plot(usa, main = "USA") plot(mainland_usa, main = "Conterminous USA") plot(contin_usa, main = "Continental USA") # import a UK map and get Great Britain: uk <- geodata::gadm("United Kingdom", path = tempdir()) great_britain <- selectLargest(uk, dissolve = TRUE) plot(uk, main = "UK") plot(great_britain, main = "Great Britain") # import a Portugal + Spain map and get the Iberian Peninsula: ptes <- geodata::gadm(c("Portugal", "Spain"), path = tempdir()) iberia <- selectLargest(ptes, dissolve = TRUE) plot(ptes, main = "Portugal and Spain") plot(iberia, main = "Iberian Peninsula") As usual, feedback is welcome! ### Share this: * Share on X (Opens in new window) X * Share on Facebook (Opens in new window) Facebook * Like Loading... ### _Related_

Calculate geometric attributes of spatial polygons including area, perimeter, compactness, elongation, orientation (bearing), fractal dimension, and various shape indices. The package relies heavily on 'terra' methods and vector data objects &lt;<a href="https://github.com/rspatial/terra" target="_top">https://github.com/rspatial/terra</a>&gt;.

Calculate geometric attributes of spatial polygons including area, perimeter, compactness, elongation, orientation (bearing), fractal dimension, and various shape indices. The package relies heavily on 'terra' methods and vector data objects &lt;<a href="https://github.com/rspatial/terra" target="_top">https://github.com/rspatial/terra</a>&gt;.

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