heatmap = {
let line = vl.markRule({strokeWidth:4})
.data([{'threshold':1963}])
.encode(vl.x().fieldO('threshold'))
let heatmap = vl.markRect({stroke: "white"})
.data(data)
.encode(
vl.x().fieldO('YEAR').axis({ticks: false, title:false}),
vl.y().fieldN('state').axis({ticks: false, title:false}),
vl.color().fieldQ('incidence').scale(colorscale).legend(null),
vl.tooltip(['state', 'YEAR', 'incidence'])
)
.width(650)
.height(450)
return vl.layer([heatmap, line]).render()
}