Plot.plot({
marks: [
Plot.dot(maples2003, {x: "stemLength", y: "stemMass", fill: "watershed"}),
Plot.linearRegressionY(maples2003,{x:"stemLength", y:"stemMass", fill:"watershed"}),
Plot.frame()
],
x:{label: "stem length"},
y:{label: "stem mass"},
color:{legend:true}
})