le = 'rgba(0, 0, 0, 0.1)';
        context.arc(polygon.x, polygon.y,
            polygon.radius + DEGREE_OUTER_RING_MARGIN,
            0, Math.PI*2, true);
    }

    function drawDegreeAnnotations(polygon) {
        var radius = polygon.radius + DEGREE_RING_MARGIN;

        context.save();
        context.fillStyle = DEGREE_ANNOTATIONS_FILL_STYLE;
        context.font = DEGREE_ANNOTATIONS_TEXT_SIZE + 'px Helvetica';

        for (var angle=0; angle < 2*Math.PI; angle += Math.PI/8) {
            context.be