Here's an example of one way you could implement an elliptical marker template:

var data = [{
                x: 2, y: 5, value1: 3, value2: 8
            }, {
                x: 3, y: 3, value1: 5, value2: 2
            }, {
                x: 1, y: 2, value1: 1, value2: 1
            }, {
                x: 3, y: 2, value1: 4, value2: 3
            }, {
                x: 5, y: 1, value1: 2, value2: 4
            }, {
                x: 4, y: 3, value1: 2, value2: 2
            }];

            var minRx;
            var maxRx;
            var minRy;
            var maxRy;
            var minRadius = 5;
            var maxRadius = 20;
            var ellipticalMarker = {
                passStarting: function (passInfo) {
                    maxRx = Number.MIN_VALUE;
                    minRx = Number.MAX_VALUE;
                    maxRy = Number.MIN_VALUE;
                    minRy = Number.MAX_VALUE;
                    for (var i = 0; i &lt data.length; i++) {
                        maxRx = Math.max(maxRx, data[i].value1);
                        minRx = Math.min(minRx, data[i].value1);
                        maxRy = Math.max(maxRy, data[i].value2);
                        minRy = Math.min(minRy, data[i].value2);
                    }
                },
                measure: function (measureInfo) {
                    var item = measureInfo.data.item(),
                    width = ((item.value1 - minRx) / (maxRx - minRx)) * (maxRadius - minRadius) + minRadius,
                    height = ((item.value2 - minRy) / (maxRy - minRy)) * (maxRadius - minRadius) + minRadius;

                    measureInfo.width = width;
                    measureInfo.height = height;
                },
                render: function (renderInfo) {
                    var ctx = renderInfo.context,
                    x = renderInfo.xPosition,
                    y = renderInfo.yPosition,
                    item = renderInfo.data.item(),
                    width = renderInfo.availableWidth,
                    height = renderInfo.availableHeight;

                    ctx.fillStyle = renderInfo.data.actualItemBrush().fill();
                    ctx.strokeStyle = renderInfo.data.outline().fill();
                    ctx.lineWidth = 1.0 / Math.max(width, height);

                    ctx.save();
                    ctx.translate(x, y);
                    ctx.scale(width, height);
                    ctx.translate(-x, -y);
                    ctx.beginPath();

                    ctx.arc(x, y, 1, 0, 2.0 * Math.PI, false);

                    ctx.fill();
                    ctx.stroke();
                    ctx.restore();
                }
            };

            $("#container").igDataChart({
                width: "500px",
                height: "500px",
                dataSource: data,
                axes: [{
                    name: "xAxis",
                    type: "numericX",
                    minimumValue: 0,
                    maximumValue: 8
                },
                {
                    name: "yAxis",
                    type: "numericY",
                    minimumValue: 0,
                    maximumValue: 8
                }],
                series: [{
                    name: "series1",
                    title: "Test Series",
                    type: "scatter",
                    xAxis: "xAxis",
                    yAxis: "yAxis",
                    xMemberPath: "x",
                    yMemberPath: "y",
                    markerTemplate: ellipticalMarker,
                    showTooltip: true,
                    tooltipTemplate: "tooltipTemplate"
                }],
                horizontalZoomable: true,
                verticalZoomable: true,
                windowResponse: "immediate",
                overviewPlusDetailPaneVisibility: "visible"
            });
        });

Hope this helps!

-Graham