Mapnik中使用XML定义线状要素的样式（dash）

 <Map background-color="#efefef" srs="+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs">
    <Style name="My Style">
        <Rule>
            <LineSymbolizer stroke="rgb(50%,50%,50%)" stroke-dasharray="8,20"/>
            <Filter>[id] = 1</Filter>
        </Rule>
    </Style>
    <Style name="My Style2">
        <Rule>
            <LineSymbolizer stroke="rgb(50%,50%,50%)" stroke-width="8" stroke-dasharray="8,20"/>
            <Filter>[id] = 2</Filter>
        </Rule>
    </Style>
    <Style name="My Style3">
        <Rule>
            <LineSymbolizer stroke="rgb(50%,50%,50%)" stroke-width="3" stroke-dasharray="6,6"/>
            <Filter>[id] = 3</Filter>
        </Rule>
    </Style>
    <Style name="My Style4">
        <Rule>
            <LineSymbolizer stroke="#000000" stroke-width="2" stroke-linejoin="miter"/>
        </Rule>
    </Style>
    <Layer name="world" srs="+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs">
        <StyleName>My Style</StyleName>
        <Datasource>
            <Parameter name="type">shape</Parameter>
            <Parameter name="file">/gdata/fig_data/fig_data_line3.shp</Parameter>
        </Datasource>
    </Layer>
    <Layer name="world" srs="+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs">
        <StyleName>My Style2</StyleName>
        <Datasource>
            <Parameter name="type">shape</Parameter>
            <Parameter name="file">/gdata/fig_data/fig_data_line3.shp</Parameter>
        </Datasource>
    </Layer>
    <Layer name="world" srs="+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs">
        <StyleName>My Style3</StyleName>
        <Datasource>
            <Parameter name="type">shape</Parameter>
            <Parameter name="file">/gdata/fig_data/fig_data_line3.shp</Parameter>
        </Datasource>
    </Layer>
</Map>