Plot.plot({
projection: "albers",
r: {range: [0, 16]},
color: {scheme: "spectral", label: "First year opened", legend: true},
marks: [
Plot.geo(statemesh, {strokeOpacity: 0.5}),
Plot.geo(nation),
Plot.dot(walmarts, Plot.hexbin({r: "count", fill: "min"}, {x: "longitude", y: "latitude", fill: "date"}))
]
})