// step 1
var es : EllipseSymbol = new EllipseSymbol();
var ellipse : GeoEllipse = new GeoEllipse();
ellipse.center = map.toMapUnits( 300, 200);
ellipse.height = map.convertDistance( 120, MeasureUnit.rmPixels, MeasureUnit.rmMapUnits);
ellipse.width = map.convertDistance( 200, MeasureUnit.rmPixels, MeasureUnit.rmMapUnits);
es.setEllipse(ellipse);

// step 2	
var cLayer : CosmeticLayer = map.getCosmeticLayer();

// step 3
var symbol : Symbol = es.getSymbol();

// step 4
var color : int = new Color(0, 0, 255).getRGB(); // blue
symbol.setColor(Symbol.rmBrushColor, color);
symbol.setBrushStyle("brush:bdiagonal");

// step 5
cLayer.getEllipses().add(es);