function exports(_selection) {
            _selection.each(function(){
                chartWidth = width - margin.left - margin.right;
                chartHeight = height - margin.top - margin.bottom;

                buildSVG(this);
                drawTooltip();
            });
        }
This function creates the graph using the selection as container
@param {D3Selection} _selection A d3 selection that represents
                                 the container(s) where the chart(s) will be rendered