var zoom = d3.zoom().on("zoom", zooming);
vis = svg.append("svg:svg")
.attr("width", width)
.attr("height", height)
.call(zoom) // here
.call(zoom.transform, d3.zoomIdentity.translate(100, 50).scale(0.5))
.append("svg:g")
.attr("transform","translate(100,50) scale(.5,.5)");