mapnik/tests/data/good_maps/bounds_clipping.xml

<!-- without maximum-extent this will drop features if a 
     buffer_size is used of >= 128 which can be simulated with:
     
a tile request like: /2/0/1.png

or using nik2img:

nik2img.py tests/data/good_maps/bounds_clipping.xml t.png -e -20037508.34 -5009377.085697313 -5009377.08569731 15028131.25709193 -d 256 256

no buffer can be simulated with:

nik2img.py tests/data/good_maps/bounds_clipping.xml t.png -d 256 256 -e -20037508.342789244 0 -10018754.171394622 10018754.17139462

+proj=krovak +lat_0=49.5 +lon_0=24.83333333333333 +alpha=30.28813975277778 +k=0.9999 +x_0=0 +y_0=0 +ellps=bessel +units=m +towgs84=498.17,136.89,510.08,6.007,4.343,3.831,3.38 +no_defs

-->

<Map 
  srs="+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs +over" 
  minimum-version="2.0.0" 
  buffer-size="128"
  maximum-extent="-20037508.34,-20037508.34,20037508.34,20037508.34"
>

  <Style name="style">
     <Rule>
        <PolygonSymbolizer fill="darkred"/>
     </Rule>
    
   </Style>

  <!-- layer in standard mercator: being protected into 
       spherical mercator makes it prone to feature loss
       when using map buffer
  -->
  <Layer 
      name="countries" 
      srs="+proj=merc +lon_0=0 +k=1 +x_0=0 +y_0=0 +ellps=WGS84 +datum=WGS84 +units=m +no_defs"
  >
    <StyleName>style</StyleName>
    <Datasource>
      <Parameter name="type">shape</Parameter>
      <Parameter name="file">../shp/world_merc2.shp</Parameter>
    </Datasource>
  </Layer>

</Map>