circles = viz.select("#layer1").selectAll(".mycircle")
.data(data)
.join("circle")
.classed("mycircle", true)
.attr("cx",d => d.value * 100)
.attr("cy", 150)
.attr("r", d => d.value * 10)
.style("fill","steelblue")
.on("mousemove", (e,d) => tooltip.show(e,d,ttOptions))
.on("mouseout", () => tooltip.hide())