图示数据

本示例内容可以参考CaseStudy目录下的文件"地图.Table"的示例十三。

本节的任务是用颜色图示各省市的人均GDP，人均GDP越高，颜色越深：

示例一

1、将Map控件的"地图来源"属性设置为"None"

2、将窗口的AfterLoad事件代码设置为：

Dim map As GeoMap = e.Form.Controls("Map1").GeoMap
Dim layer As New VectorLayer()
map.Layers.Add(layer)
layer.Style.Stroke.Color = Color.Gray
Dim minValue As Double = DataTables("省").Compute("Min(人均GDP)")
Dim maxValue As Double = DataTables("省").Compute("Max(人均GDP)")
Dim minColor As Color = Color.FromArgb(230, 247, 255) ' 浅蓝
Dim maxColor As Color = Color.FromArgb(74, 0, 114) '深紫
For Each dr As DataRow In DataTables("行政区 域").Select("level= 1") '绘制省级行政区
    Dim polygon As VectorPolygon = map.CreatePolygon(dr("geometry"))
    layer.Items.Add(Polygon)
    Dim sr As DataRow = DataTables("省").Find("省代码 = '" & dr("adcode") & "'")
    If sr IsNot Nothing Then
        Dim value As Double = sr("人均GDP")
        Dim radio As Double
        radio = (value - minValue) / (maxValue - minValue)
        Dim red As Byte = minColor.R + (CInt(maxColor.R) - CInt(minColor.R)) * radio
        Dim green As Byte = minColor.G + CInt((maxColor.G) - CInt(minColor.G)) * radio
        Dim blue As Byte = minColor.B + (CInt(maxColor.B) - CInt(minColor.B)) * radio
        polygon.Style.BackColor = Color.FromArgb(red, green, blue)
        polygon.Tag = sr("省") & ":" & sr("人均GDP")
    End If
Next

示例二

如果希望用颜色深浅表示市级行政区域的人均GDP(参考示例十四)，可以将代码改为：

Dim map As GeoMap = e.Form.Controls("Map1").GeoMap
Dim layer As New VectorLayer()
map.Layers.Add(layer)
layer.Style.Stroke.Color = Color.Gray
Dim minValue As Double = DataTables("市").Compute("Min(人均GDP)")
Dim maxValue As Double = DataTables("市").Compute("Max(人均GDP)")
Dim minColor As Color = Color.FromArgb(230, 247, 255) ' 浅蓝
Dim maxColor As Color = Color.FromArgb(74, 0, 114) '深紫
For Each dr As DataRow In DataTables("行政区域").Select("level= 2") '绘制市级行政区
    Dim polygon As VectorPolygon = map.CreatePolygon(dr("geometry"))
    layer.Items.Add(Polygon)
    Dim sr As DataRow = DataTables("市").Find("市代码 = '" & dr("adcode") & "'")
    If sr IsNot Nothing Then
        Dim value As Double = sr("人均GDP")
        Dim radio As Double
        radio = (value - minValue) / (maxValue - minValue)
        Dim red As Byte = minColor.R + (CInt(maxColor.R) - CInt(minColor.R)) * radio
        Dim green As Byte = minColor.G + CInt((maxColor.G) - CInt(minColor.G)) * radio
        Dim blue As Byte = minColor.B + (CInt(maxColor.B) - CInt(minColor.B)) * radio
        polygon.Style.BackColor = Color.FromArgb(red, green, blue)
        polygon.Tag = dr("name") & ":" & sr("人均GDP")
    Else
        polygon.Tag = dr("name")
    End If
Next

绘制的地图如下 ，出现一些白色区域是因为GDP数据不全：