FlexChartには、マウスで選択した領域を拡大表示（ズーム）するための機能は備わっていません。代替策として、MouseDownおよびMouseUpイベントで、選択した領域の開始点／終了点を取得し、この値をもとに、AxisXのMin／Max、およびAxisYのMin／Maxを調整して拡大表示させることができます。

ただしこのままでは、FlexChart上に描画した図形注釈は、レイヤーが異なるためリサイズされません。
対応方法として、Renderedイベント内で図形注釈のサイズを設定することにより、マウスでのズームに連動させる手段が考えられます。

以下に、選択した領域を、四角形の注釈も含めてズームするコードを記載します。
    ※サンプルを実行し、注釈を含む領域を Ctrlキー ＋ マウスドラッグで選択してください。



◎サンプルコード（VB）

Imports C1.Chart
Imports C1.Win.Chart

Public Class Form1

    Private AnnotationLayer01 As Annotation.AnnotationLayer
    Private p1 As Point
    Private p2 As Point

    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        'データの作成
        Dim dt As New DataTable()
        With dt
            .Columns.Add("X", GetType(Int32))
            .Columns.Add("Y", GetType(Int32))
            'Dim r As New Random()
            For i = 0 To 5
                '.Rows.Add(i, r.Next(1, 20))
                .Rows.Add(i, i * 4)
            Next
            .AcceptChanges()
        End With

        ' シリーズの作成
        Dim series1 As New Series() With {
            .BindingX = "X",
            .Binding = "Y",
            .DataSource = dt
        }

        ' チャートの設定
        With FlexChart1
            .Series.Clear()
            .Series.Add(series1)
            .ChartType = ChartType.LineSymbols
            .AxisY.Max = 20
            .AxisY.Min = 0
            .PlotMargin = New Padding(40, 40, 40, 40)
            .ToolTip.Active = False
        End With

        ' 注釈レイヤの作成
        AnnotationLayer01 = New Annotation.AnnotationLayer(FlexChart1)
        ' 四角形の注釈
        Dim annRect As New Annotation.Rectangle("")
        With annRect
            .Style.FillColor = Color.FromArgb(100, Color.Aqua)
            .Style.StrokeColor = Color.Black
            .Style.StrokeWidth = 1
            .Style.LinePattern = LinePatternEnum.Solid
        End With
        AnnotationLayer01.Annotations.Add(annRect)
    End Sub

    Private Sub FlexChart1_Rendered(sender As Object, e As C1.Win.Chart.RenderEventArgs) Handles FlexChart1.Rendered
        ' ズーム処理：矩形の描画
        Dim rect As New Rectangle(Math.Min(p1.X, p2.X), Math.Min(p1.Y, p2.Y), Math.Abs(p1.X - p2.X), Math.Abs(p1.Y - p2.Y))
        e.Graphics.DrawRectangle(Pens.Red, rect)

        ' 注釈の描画
        Dim annRect = DirectCast(AnnotationLayer01.Annotations(0), Annotation.Rectangle)
        With annRect
            .Attachment = Annotation.AnnotationAttachment.DataCoordinate
            .Location = New PointF(2 / 2.0F, (FlexChart1.AxisY.ActualMax + FlexChart1.AxisY.ActualMin) / 2.0F)
            .Height = FlexChart1.AxisY.Convert(0) - FlexChart1.AxisY.Convert(20)
            .Width = FlexChart1.AxisX.Convert(2) - FlexChart1.AxisX.Convert(0)
        End With
    End Sub

    ' ズーム処理
    Private Sub FlexChart1_KeyDown(sender As Object, e As KeyEventArgs) Handles FlexChart1.KeyDown
        If e.KeyCode = Keys.F1 Then
            e.SuppressKeyPress = True

            ' F1キーでズームのリセット
            With FlexChart1
                .BeginUpdate()
                .AxisX.Min = Double.NaN
                .AxisY.Min = 0
                .AxisX.Max = Double.NaN
                .AxisY.Max = 20
                .EndUpdate()
            End With
        End If
    End Sub

    ' ズーム処理
    Private Sub FlexChart1_MouseDown(sender As Object, e As MouseEventArgs) Handles FlexChart1.MouseDown
        If Control.ModifierKeys = Keys.Control Then
            ' 開始位置の保存
            p1 = e.Location
            p2 = Point.Empty
        End If
    End Sub

    ' ズーム処理
    Private Sub FlexChart1_MouseMove(sender As Object, e As MouseEventArgs) Handles FlexChart1.MouseMove
        If e.Button = MouseButtons.Left AndAlso Control.ModifierKeys = Keys.Control Then
            ' 現在位置の保存
            p2 = e.Location

            ' 現在の矩形の描画
            FlexChart1.Invalidate()
        End If
    End Sub

    ' ズーム処理
    Private Sub FlexChart1_MouseUp(sender As Object, e As MouseEventArgs) Handles FlexChart1.MouseUp
        If Control.ModifierKeys = Keys.Control Then
            With FlexChart1
                ' 軸範囲の変更
                Dim p1 As Double() = New Double() { .AxisX.ConvertBack(Me.p1.X), .AxisY.ConvertBack(Me.p1.Y)}
                Dim p2 As Double() = New Double() { .AxisX.ConvertBack(Me.p2.X), .AxisY.ConvertBack(Me.p2.Y)}
                .BeginUpdate()
                .AxisX.Min = Math.Min(p1(0), p2(0))
                .AxisY.Min = Math.Min(p1(1), p2(1))
                .AxisX.Max = Math.Max(p1(0), p2(0))
                .AxisY.Max = Math.Max(p1(1), p2(1))
                .EndUpdate()

                ' 変数の初期化
                Me.p1 = Point.Empty
                Me.p2 = Point.Empty
            End With
        End If
    End Sub
End Class

◎サンプルコード（C#）

using C1.Chart;
using C1.Win.Chart;
using C1.Win.Chart.Annotation;

namespace prj_Anno_enLarge
{
    public partial class Form1 : Form
    {
        C1.Win.Chart.Annotation.AnnotationLayer AnnotationLayer01;
        Point p1;
        Point p2;
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            //データの作成
            DataTable dt = new DataTable();
            dt.Columns.Add("X", typeof(Int32));
            dt.Columns.Add("Y", typeof(Int32));
            for (int i = 0; i < 6; i++)
            {
                dt.Rows.Add(i, i * 4);
            }
            dt.AcceptChanges();

            // シリーズの作成
            Series series1 = new Series()
            {
                BindingX = "X",
                Binding = "Y",
                DataSource = dt
            };

            // チャートの設定
            flexChart1.Series.Clear();
            flexChart1.Series.Add(series1);
            flexChart1.ChartType = ChartType.LineSymbols;
            flexChart1.AxisY.Max = 20;
            flexChart1.AxisY.Min = 0;
            flexChart1.PlotMargin = new Padding(40, 40, 40, 40);
            flexChart1.ToolTip.Active = false;

            // 注釈レイヤの作成
            AnnotationLayer01 = new AnnotationLayer(flexChart1);
            // 四角形の注釈
            C1.Win.Chart.Annotation.Rectangle annRect = new C1.Win.Chart.Annotation.Rectangle("");
            annRect.Style.FillColor = Color.FromArgb(100, Color.Aqua);
            annRect.Style.StrokeColor = Color.Black;
            annRect.Style.StrokeWidth = 1;
            annRect.Style.LinePattern = LinePatternEnum.Solid;

            AnnotationLayer01.Annotations.Add(annRect);

        }

        private void flexChart1_Rendered(object sender, RenderEventArgs e)
        {
            // ズーム処理：矩形の描画
            System.Drawing.Rectangle rect = new System.Drawing.Rectangle(Math.Min(p1.X, p2.X), Math.Min(p1.Y, p2.Y), Math.Abs(p1.X - p2.X), Math.Abs(p1.Y - p2.Y));
            e.Graphics.DrawRectangle(Pens.Red, rect);

            //注釈の描画
           C1.Win.Chart.Annotation.Rectangle annRect = (C1.Win.Chart.Annotation.Rectangle)AnnotationLayer01.Annotations[0];

            annRect.Attachment = C1.Chart.Annotation.AnnotationAttachment.DataCoordinate;
            annRect.Location = new PointF(2 / 2.0F, (float)(flexChart1.AxisY.ActualMax + flexChart1.AxisY.ActualMin) / 2.0F);
            annRect.Height = flexChart1.AxisY.Convert(0) - flexChart1.AxisY.Convert(20);
            annRect.Width = flexChart1.AxisX.Convert(2) - flexChart1.AxisX.Convert(0);
        }

        private void flexChart1_KeyDown(object sender, KeyEventArgs e)
        {
            if ((e.KeyCode == Keys.F1))
            {
                e.SuppressKeyPress = true;

                // F1キーでズームのリセット
                flexChart1.BeginUpdate();
                flexChart1.AxisX.Min = Double.NaN;
                flexChart1.AxisY.Min = 0;
                flexChart1.AxisX.Max = Double.NaN;
                flexChart1.AxisY.Max = 20;
                flexChart1.EndUpdate();
            }
        }

        // ズーム処理
        private void flexChart1_MouseDown(object sender, MouseEventArgs e)
        {
            if ((Control.ModifierKeys == Keys.Control))
            {
                // 開始位置の保存
                p1 = e.Location;
                p2 = Point.Empty;
            }
        }

        // ズーム処理
        private void flexChart1_MouseMove(object sender, MouseEventArgs e)
        {
            if (((e.Button == MouseButtons.Left) && (Control.ModifierKeys == Keys.Control)))
            {
                // 現在位置の保存
                p2 = e.Location;
                // 現在の矩形の描画
                flexChart1.Invalidate();
            }
        }

        // ズーム処理
        private void flexChart1_MouseUp(object sender, MouseEventArgs e)
        {
            if ((Control.ModifierKeys == Keys.Control))
            {
                //  軸範囲の変更
                double[] p1 = new double[] {flexChart1.AxisX.ConvertBack(this.p1.X), flexChart1.AxisY.ConvertBack(this.p1.Y)};
                double[] p2 = new double[] {flexChart1.AxisX.ConvertBack(this.p2.X), flexChart1.AxisY.ConvertBack(this.p2.Y)};

                flexChart1.BeginUpdate();
                flexChart1.AxisX.Min = Math.Min(p1[0], p2[0]);
                flexChart1.AxisY.Min = Math.Min(p1[1], p2[1]);
                flexChart1.AxisX.Max = Math.Max(p1[0], p2[0]);
                flexChart1.AxisY.Max = Math.Max(p1[1], p2[1]);
                flexChart1.EndUpdate();

                // 変数の初期化
                this.p1 = Point.Empty;
                this.p2 = Point.Empty;
            }
        }
    }
}