...

		var xScale = d3.scale.linear()
			.domain([200,1000])
			.range([25,375]);

		var yScale = d3.scale.linear()
			.domain([0, d3.max(data, function(x){return x.height})])
			.range([150,25]);

		svg.selectAll("circle")
			.data(data)
			.enter()
			.append("circle")
			.attr("r", 10)
			.attr("cx", function(x){return xScale(x.weight)})
			.attr("cy", function(x){return yScale(x.height)})
			.style("fill", function(x){return x.colour});