mapnik/tests/visual_tests/styles/lines-shield.xml

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE Map>
<Map background-color="white" srs="+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs">
    <Parameters>
        <Parameter name="sizes">800, 800; 600, 600; 400, 400; 200, 200</Parameter>
        <Parameter name="bbox">-0.05, -0.01, 0.95, 0.01</Parameter>
    </Parameters>

    <Layer name="layer" srs="+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs">
        <StyleName>My Style</StyleName>
        <Datasource>
            <Parameter name="type">csv</Parameter>
            <Parameter name="file">../data/lines.csv</Parameter>
        </Datasource>
    </Layer>

    <Style name="My Style">
        <Rule>
            <Filter>[mapnik::geometry_type]=linestring</Filter>
            <LineSymbolizer stroke-width="1" stroke="blue"/>
            <ShieldSymbolizer face-name="DejaVu Sans Book" size="16" placement="line" file="../../data/svg/crosshair16x16.svg" spacing="30">'X'</ShieldSymbolizer>
        </Rule>
    </Style>

</Map>