North America Precipitation Map

Mix.install([
  {:plotly_ex, "~> 0.3"},
  {:kino, "~> 0.18"},
  {:req, "~> 0.5"}
])

Section

marker.color: as a numeric list combined with colorscale: maps the precipitation value to a color. showscale: true adds a color bar legend.

alias Plotly.{Figure, Scattergeo}

url = "https://raw.githubusercontent.com/plotly/datasets/master/2015_06_30_precipitation.csv"
body = Req.get!(url).body

[header | rows] = String.split(body, "\n", trim: true)
keys = String.split(header, ",") |> Enum.map(&String.trim/1)

data =
  rows
  |> Enum.map(fn row ->
    values = String.split(row, ",")
    Enum.zip(keys, values) |> Map.new()
  end)
  |> Enum.filter(fn r ->
    match?({_, _}, Float.parse(r["Lat"] || "")) and
    match?({_, _}, Float.parse(r["Lon"] || "")) and
    match?({_, _}, Float.parse(r["Globvalue"] || ""))
  end)

lat = Enum.map(data, &(elem(Float.parse(&1["Lat"]), 0)))
lon = Enum.map(data, &(elem(Float.parse(&1["Lon"]), 0)))
precip = Enum.map(data, &(elem(Float.parse(&1["Globvalue"]), 0)))

Figure.new()
|> Figure.add_trace(
  Scattergeo.new(
    lat: lat,
    lon: lon,
    mode: "markers",
    marker: %{
      size: 5,
      color: precip,
      colorscale: "Portland",
      reversescale: false,
      cmin: 0,
      cmax: Enum.max(precip),
      showscale: true,
      colorbar: %{title: %{text: "Precipitation (in)"}}
    }
  )
)
|> Figure.update_layout(
  title: "North America Precipitation — June 30, 2015",
  geo: %{
    scope: "north america",
    showland: true,
    landcolor: "#EAEAAE",
    showocean: true,
    oceancolor: "#BDDDE4",
    showlakes: true,
    lakecolor: "#BDDDE4",
    lataxis: %{range: [15, 75]},
    lonaxis: %{range: [-180, -50]}
  }
)
|> Plotly.show()