Multiple Filled Areas with a Scattermap Trace

Mix.install([
  {:plotly_ex, "~> 0.3"},
  {:kino, "~> 0.18"}
])

Section

Each polygon is a separate Scattermap trace with its own fill: "toself" and fillcolor:. This gives each area an independent legend entry and color.

alias Plotly.{Figure, Scattermap}

# Approximate bounding boxes for western US states
states = [
  {"California", [42.0, 42.0, 32.5, 32.5, 42.0], [-124.4, -114.1, -114.1, -124.4, -124.4], "rgba(255,0,0,0.2)", "red"},
  {"Nevada", [42.0, 42.0, 35.0, 35.0, 42.0], [-120.0, -114.0, -114.0, -120.0, -120.0], "rgba(0,255,0,0.2)", "green"},
  {"Arizona", [37.0, 37.0, 31.3, 31.3, 37.0], [-114.8, -109.0, -109.0, -114.8, -114.8], "rgba(0,0,255,0.2)", "blue"},
  {"Utah", [42.0, 42.0, 37.0, 37.0, 42.0], [-114.1, -109.0, -109.0, -114.1, -114.1], "rgba(255,165,0,0.2)", "orange"}
]

fig = Figure.new()

fig =
  Enum.reduce(states, fig, fn {name, lats, lons, fill, line_color}, acc ->
    Figure.add_trace(acc,
      Scattermap.new(
        lat: lats,
        lon: lons,
        mode: "lines",
        fill: "toself",
        fillcolor: fill,
        line: %{color: line_color, width: 2},
        name: name
      )
    )
  end)

fig
|> Figure.update_layout(
  title: "Multiple Filled Areas — Western US States",
  map: %{
    style: "open-street-map",
    center: %{lat: 38.5, lon: -115.0},
    zoom: 4
  }
)
|> Plotly.show()