mapnik/tests/visual_tests/styles/marker-on-line-spacing-eq-width.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">600,400</Parameter>
    </Parameters>
    <Layer name="layer" srs="+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs">
        <StyleName>alpha</StyleName>
        <Datasource>
            <Parameter name="type">csv</Parameter>
            <Parameter name="inline">
            wkt
            "LINESTRING(0 0, 10 2)"
            </Parameter>
        </Datasource>
    </Layer>
    <Layer name="layer" srs="+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs">
        <StyleName>beta</StyleName>
        <Datasource>
            <Parameter name="type">csv</Parameter>
            <Parameter name="inline">
            wkt
            "LINESTRING(0 2, 10 4)"
            </Parameter>
        </Datasource>
    </Layer>
    <Layer name="layer" srs="+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs">
        <StyleName>gamma</StyleName>
        <Datasource>
            <Parameter name="type">csv</Parameter>
            <Parameter name="inline">
            wkt
            "LINESTRING(0 4, 10 6)"
            </Parameter>
        </Datasource>
    </Layer>

    <Style name="alpha">
        <Rule>
            <MarkersSymbolizer file="shape://ellipse" allow-overlap="false" width="20" height="20" placement="line" spacing="25"/>
            <LineSymbolizer stroke-width="0.2" stroke="#ff0000" />
        </Rule>
    </Style>
    <Style name="beta">
        <Rule>
            <MarkersSymbolizer file="shape://ellipse" allow-overlap="false" width="20" height="20" placement="line" spacing="20"/>
            <LineSymbolizer stroke-width="0.2" stroke="#ff0000" />
        </Rule>
    </Style>
    <Style name="gamma">
        <Rule>
            <MarkersSymbolizer file="shape://ellipse" allow-overlap="false" width="20" height="20" placement="line" spacing="15"/>
            <LineSymbolizer stroke-width="0.2" stroke="#ff0000" />
        </Rule>
    </Style>
</Map>