viewof parks = {
const landmass = vl.markGeoshape()
.data(vl.topojson("https://unpkg.com/us-atlas@3/nation-10m.json").feature("nation"))
.encode(vl.stroke().value("lightgray"),
vl.color().value(null));
const points = vl.markCircle()
.data(pota)
.encode(
vl.longitude().fieldQ("longitude"),
vl.latitude().fieldQ("latitude"),
vl.color().fieldO("mode"));
return vl.layer(landmass, points)
.project(vl.projection("albersUsa"))
.render()
}