d3.select("svg")
.attr("viewBox", "0 0 600 600")
.attr("width", "1280")
.attr("preserveAspectRatio", "none");
http://www.w3.org/TR/SVG/coords.html#ViewBoxAttribute
Mike
Look at this example and try resizing your window: http://christopheviau.com/d3_tutorial/d3_examples/ . Maybe it can help.