function zoomWithSlider(scale) {
var svg = d3.select("body").select("svg");
var container = svg.select("g");
var h = svg.attr("height"), w = svg.attr("width");
// Note: works only on the <g> element and not on the <svg> element
// which is a common mistake
container.attr("transform",
"translate(" + w/2 + ", " + h/2 + ") " +
"scale(" + scale + ") " +
"translate(" + (-w/2) + ", " + (-h/2) + ")");