Base Tiles from the USGS, Radar Overlay from Environment Canada

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

Section

Multiple entries in layout.map.layers stack in order — first entry is bottom-most. Here the USGS topo map is the base, and the Environment Canada radar is the overlay. Note: the radar layer is a live WMS service and may not always be available.

alias Plotly.{Figure, Scattermap}

Figure.new()
|> Figure.add_trace(
  Scattermap.new(
    lat: [45.4215],
    lon: [-75.6972],
    mode: "markers",
    text: ["Ottawa"],
    marker: %{size: 12, color: "yellow"}
  )
)
|> Figure.update_layout(
  title: "USGS Base + Environment Canada Radar Overlay",
  map: %{
    style: "white-bg",
    center: %{lat: 47.0, lon: -85.0},
    zoom: 4,
    layers: [
      %{
        below: "traces",
        sourcetype: "raster",
        source: ["https://basemap.nationalmap.gov/arcgis/rest/services/USGSTopo/MapServer/tile/{z}/{y}/{x}"],
        opacity: 0.9
      },
      %{
        below: "traces",
        sourcetype: "raster",
        source: ["https://geo.weather.gc.ca/geomet?SERVICE=WMS&VERSION=1.3.0&REQUEST=GetMap&BBOX={bbox-epsg-3857}&CRS=EPSG:3857&WIDTH=1000&HEIGHT=1000&LAYERS=RADAR_1KM_RDBR&TILED=true&FORMAT=image/png"],
        opacity: 0.7
      }
    ]
  }
)
|> Plotly.show()