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SharpMap 學習筆記(一)：從零開始建立 Web GIS 地圖顯示基礎架構

編輯：關於.NET

緣起與技術棧

公司產品需整合電子地圖，選用開源專案 SharpMap（簡單易用、適合入門），輔以 MapWindow GIS 製作 Shapefile、NetTopologySuite 補足空間運算。

前端：AjaxMapControl 佈局

<smap:AjaxMapControl width="1600px" Height="600px" id="ajaxMap" runat="server" 
    OnClickEvent="MapClicked" onmouseout="toolTip();" OnViewChange="ViewChanged" 
    CssClass="Ly" UseCache="false" OnViewChanging="ViewChanging" ZoomSpeed="1" />

後端：地圖初始化完整代碼

public static SharpMap.Map InitializeMap(Size size) {
    var map = new SharpMap.Map(size);

    // 國家圖層
    var layCountries = new VectorLayer("Countries");
    layCountries.DataSource = new ShapeFile(Server.MapPath(@"~\App_data\countries.shp"), true);
    layCountries.Style.Fill = new SolidBrush(Color.Green);
    layCountries.Style.Outline = Pens.Black; layCountries.Style.EnableOutline = true;
    layCountries.SRID = 4326;

    // 河流圖層
    var layRivers = new VectorLayer("Rivers");
    layRivers.DataSource = new ShapeFile(Server.MapPath(@"~\App_data\rivers.shp"), true);
    layRivers.Style.Line = new Pen(Color.Blue, 1);
    layRivers.SRID = 4326;

    // 城市圖層
    var layCities = new VectorLayer("Cities");
    layCities.DataSource = new ShapeFile(Server.MapPath(@"~\App_data\cities.shp"), true);
    layCities.Style.SymbolScale = 0.8f;
    layCities.MaxVisible = 40; layCities.SRID = 4326;

    // 國家標籤層
    var layLabel = new LabelLayer("Country labels");
    layLabel.DataSource = layCountries.DataSource;
    layLabel.Enabled = true; layLabel.LabelColumn = "Name";
    layLabel.Style = new LabelStyle { ForeColor = Color.White, Font = new Font(FontFamily.GenericSerif, 12), BackColor = new SolidBrush(Color.FromArgb(128, 255, 0, 0)) };
    layLabel.MaxVisible = 90; layLabel.MinVisible = 30;
    layLabel.Style.HorizontalAlignment = HorizontalAlignmentEnum.Center;
    layLabel.SRID = 4326;
    layLabel.MultipartGeometryBehaviour = MultipartGeometryBehaviourEnum.Largest;

    // 城市標籤層
    var layCityLabel = new LabelLayer("City labels");
    layCityLabel.DataSource = layCities.DataSource;
    layCityLabel.Enabled = true; layCityLabel.LabelColumn = "Name";
    layCityLabel.Style = new LabelStyle { ForeColor = Color.Black, Font = new Font(FontFamily.GenericSerif, 11) };
    layCityLabel.MaxVisible = layLabel.MinVisible;
    layCityLabel.Style.HorizontalAlignment = HorizontalAlignmentEnum.Left;
    layCityLabel.Style.VerticalAlignment = VerticalAlignmentEnum.Bottom;
    layCityLabel.Style.Offset = new PointF(3, 3);
    layCityLabel.Style.Halo = new Pen(Color.Yellow, 2);
    layCityLabel.TextRenderingHint = TextRenderingHint.AntiAlias;
    layCityLabel.SmoothingMode = SmoothingMode.AntiAlias;
    layCityLabel.SRID = 4326;
    layCityLabel.LabelFilter = LabelCollisionDetection.ThoroughCollisionDetection;
    layCityLabel.Style.CollisionDetection = true;

    // 圖層疊加順序決定繪製順序
    map.Layers.Add(layCountries);
    map.Layers.Add(layRivers);
    map.Layers.Add(layCities);
    map.Layers.Add(layLabel);
    map.Layers.Add(layCityLabel);

    map.MaximumZoom = 360;
    map.BackColor = Color.LightBlue;
    map.Zoom = 360;
    map.Center = new SharpMap.Geometries.Point(0, 0);
    return map;
}

關鍵概念解析

VectorLayer + ShapeFile：每個圖層對應一個 Shapefile 資料源，ShapeFile 實作 IProvider 介面。
Style 屬性：控制填充、外框、線條、符號等視覺樣式。
LabelLayer：共用資料源，LabelColumn 指定顯示欄位，MaxVisible/MinVisible 控制可見縮放範圍（常被忽略導致標籤消失）。
圖層順序：map.Layers.Add 順序即繪製順序，後加入者疊加在上層。

輸出地圖影像

var img = (Bitmap)map.GetMap();
context.Response.ContentType = "image/png";
using (var ms = new MemoryStream()) {
    img.Save(ms, ImageFormat.Png);
    img.Dispose();
    context.Response.OutputStream.Write(ms.ToArray(), 0, (int)ms.Length);
}