Plotting polygons defined in degrees

Specific Domains Visualization
1

I’m trying to plot the polygons from GADM.jl. I do the following:

using GeoTables
using GeoArtifacts
using Countries
using DataFrames
using Meshes
using GLMakie 
using GeoMakie

> gdf = GADM.get("FIN"; level=0)
> p = reduce(vcat, gdf.geometry)
> typeof(p.geoms[1])
 PolyArea{🌐, CoordRefSystems.GeodeticLatLon{CoordRefSystems.WGS84Latest, Unitful.Quantity{Float64, NoDims, Unitful.FreeUnits{(°,), NoDims, nothing}}}, Ring{🌐, CoordRefSystems.GeodeticLatLon{CoordRefSystems.WGS84Latest, Unitful.Quantity{Float64, NoDims, Unitful.FreeUnits{(°,), NoDims, nothing}}}, CircularArrays.CircularVector{Meshes.Point{🌐, CoordRefSystems.GeodeticLatLon{CoordRefSystems.WGS84Latest, Unitful.Quantity{Float64, NoDims, Unitful.FreeUnits{(°,), NoDims, nothing}}}}, Vector{Meshes.Point{🌐, CoordRefSystems.GeodeticLatLon{CoordRefSystems.WGS84Latest, Unitful.Quantity{Float64, NoDims, Unitful.FreeUnits{(°,), NoDims, nothing}}}}}}}, Vector{Ring{🌐, CoordRefSystems.GeodeticLatLon{CoordRefSystems.WGS84Latest, Unitful.Quantity{Float64, NoDims, Unitful.FreeUnits{(°,), NoDims, nothing}}}, CircularArrays.CircularVector{Meshes.Point{🌐, CoordRefSystems.GeodeticLatLon{CoordRefSystems.WGS84Latest, Unitful.Quantity{Float64, NoDims, Unitful.FreeUnits{(°,), NoDims, nothing}}}}, Vector{Meshes.Point{🌐, CoordRefSystems.GeodeticLatLon{CoordRefSystems.WGS84Latest, Unitful.Quantity{Float64, NoDims, Unitful.FreeUnits{(°,), NoDims, nothing}}}}}}}}}

This is not plottable by viz!() (from Meshes.jl I believe). Simply nothing is plotted. I can plot PolyAreas when the coordinates are plain numbers, not (:lat, :lon) tuples in degree units.

2

Check Optimize visualization of non-Euclidean geometries and domains · Issue #1367 · JuliaGeometry/Meshes.jl · GitHub for additional information.

The current workaround is to project the spherical geometries into “flat” Euclidean geometries before plotting, and that is already optimized:

julia> using GeoStats

julia> using GeoArtifacts

julia> import GLMakie as Mke

julia> gtb = GADM.get("FIN")
               1×3 GeoTable over 1 GeometrySet
┌─────────────┬─────────────┬───────────────────────────────┐
│    GID_0    │   COUNTRY   │           geometry            │
│ Categorical │ Categorical │         MultiPolygon          │
│  [NoUnits]  │  [NoUnits]  │ 🖈 GeodeticLatLon{WGS84Latest} │
├─────────────┼─────────────┼───────────────────────────────┤
│     FIN     │   Finland   │     Multi(2879×PolyArea)      │
└─────────────┴─────────────┴───────────────────────────────┘

julia> ptb = gtb |> Proj(Robinson)
            1×3 GeoTable over 1 GeometrySet
┌─────────────┬─────────────┬─────────────────────────┐
│    GID_0    │   COUNTRY   │        geometry         │
│ Categorical │ Categorical │      MultiPolygon       │
│  [NoUnits]  │  [NoUnits]  │ 🖈 Robinson{WGS84Latest} │
├─────────────┼─────────────┼─────────────────────────┤
│     FIN     │   Finland   │  Multi(2879×PolyArea)   │
└─────────────┴─────────────┴─────────────────────────┘

julia> viewer(ptb)

image
image730×608 35.8 KB

If you have the time and skill to contribute, please reach out in our community channels.

3

Ok this works. Although the color is not what I expected.

image
image331×497 15.2 KB

4

Please share the script used, otherwise it is impossible to debug. The color is assigned by the viewer or you can specify it with the lower level viz function.

I highly recommend reading the GDSJL book:

5

Another simple way to plot this is

using DataFrames
using GADM
using GeoMakie
using CairoMakie  # Or GLMakie should work
gdf = GADM.get("FIN"; depth=0) |> DataFrame

fig = Figure()
ga = GeoAxis(fig[1, 1]; dest="+proj=eqdc +datum=WGS84 +lat_1=60 +lat_2=71")
poly!(ga, gdf.geom; color=:blue, strokecolor=:darkblue, strokewidth=1, shading=NoShading)
fig