Spain and Catalonia (2D)

This example downloads NUTS administrative boundaries from Eurostat GISCO and produces two separate meshes: mainland Spain (country level, NUTS-0) and Catalonia (region level, NUTS-2).

Features highlighted:

• Downloading and reading GeoJSON files from Eurostat GISCO
• Selecting features by NUTS ID and ring index
• Composing simplification algorithms with ∘: AngleFilter ∘ MinEdgeLength applies minimum-edge-length first, then removes zig-zag spikes by angle
• Using different NUTS levels (NUTS-0 vs NUTS-2) for country vs. region

NUTS levels

NUTS-0 = countries (e.g. "ES" for Spain). NUTS-2 = regions (e.g. "ES51" for Catalonia). They are distributed in separate files.

Spain	Catalonia

using GeoGmsh
using Downloads
import GeometryOps as GO

data_dir = joinpath(@__DIR__, "..", "data")
mkpath(data_dir)

Download

Two NUTS files are needed: NUTS-0 for the country outline and NUTS-2 for the regional breakdown.

base_url = "https://gisco-services.ec.europa.eu/distribution/v2/nuts/geojson/"

nuts0_url  = base_url * "NUTS_RG_01M_2024_4326_LEVL_0.geojson"
nuts0_path = joinpath(data_dir, "NUTS_RG_01M_2024_4326_LEVL_0.geojson")

nuts2_url  = base_url * "NUTS_RG_01M_2024_4326_LEVL_2.geojson"
nuts2_path = joinpath(data_dir, "NUTS_RG_01M_2024_4326_LEVL_2.geojson")

if !isfile(nuts0_path)
  println("Downloading NUTS-0 boundaries…")
  Downloads.download(nuts0_url, nuts0_path)
  println("  Saved: ", nuts0_path)
end

if !isfile(nuts2_path)
  println("Downloading NUTS-2 boundaries (~16 MB)…")
  Downloads.download(nuts2_url, nuts2_path)
  println("  Saved: ", nuts2_path)
end

Mainland Spain

The NUTS-0 "ES" feature is a MultiPolygon whose largest component (ring == 1) is the Iberian mainland.

The composed algorithm AngleFilter(tol=20°) ∘ MinEdgeLength(tol=10 km) first removes short edges (≤ 10 km), then iteratively removes vertices where the interior angle is shallower than 20°, eliminating zig-zag spikes along the coastline.

println("\n=== Spain (mainland) ===")

println("\nNUTS-0 Spain components (sorted by area):")
comps = list_components(nuts0_path)
comps = filter(row -> row.NUTS_ID == "ES", comps)
sort!(comps, :area, rev = true)
println(comps)

spain_alg = AngleFilter(tol = 20.0) ∘ MinEdgeLength(tol = 10_000.0)

geoms_to_geo(
  nuts0_path, joinpath(data_dir, "spain");
  select       = row -> row.NUTS_ID == "ES" && row.ring == 1,
  target_crs   = "EPSG:3857",
  simplify_alg = spain_alg,
  bbox_size    = 100.0,
  verbose      = true,
)

geoms_to_msh(
  nuts0_path, joinpath(data_dir, "spain");
  select       = row -> row.NUTS_ID == "ES" && row.ring == 1,
  target_crs   = "EPSG:3857",
  simplify_alg = spain_alg,
  bbox_size    = 100.0,
  mesh_size    = 2.0,
  verbose      = true,
)

Catalonia

Catalonia ("ES51") is a NUTS-2 region on the north-east coast of Spain. We use the finer NUTS-2 file, with MinEdgeLength only (the boundary is smoother at this scale so angle filtering is not needed).

println("\n=== Catalonia (ES51) ===")

println("\nNUTS-2 Catalonia components (sorted by area):")
comps2 = list_components(nuts2_path)
comps2 = filter(row -> row.NUTS_ID == "ES51", comps2)
sort!(comps2, :area, rev = true)
println(comps2)

geoms_to_geo(
  nuts2_path, joinpath(data_dir, "catalonia");
  select       = row -> row.NUTS_ID == "ES51" && row.ring == 1,
  target_crs   = "EPSG:3857",
  simplify_alg = MinEdgeLength(tol = 10_000.0),
  bbox_size    = 100.0,
  verbose      = true,
)

geoms_to_msh(
  nuts2_path, joinpath(data_dir, "catalonia");
  select       = row -> row.NUTS_ID == "ES51" && row.ring == 1,
  target_crs   = "EPSG:3857",
  simplify_alg = MinEdgeLength(tol = 10_000.0),
  bbox_size    = 100.0,
  mesh_size    = 2.0,
  verbose      = true,
)

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