how to make mapnik style raster, not just render as solid color

Question

I have set up Mapnik with mod_tile and renderd. I replaced the default osm.xml file with my own xml file, which is shown below.

My problem is that all images are being created as solid blue tiles as per the #8db0d3 background-color param in the xml file. I can change that, and the tiles will change their colors, so I know that the setup is paying attention to the xml file.

What do I need to do to make Mapnik render tiles for the specified Layer according to the given Style, and not just as a default solid background color? I expect solid-color tiles for most of the world, just not for the small area along the Connecticut coast that the given image details.

I feel like it might have something to do with the srs parameter to the map and/or layer, but I am not sure.

I can run a python script using this xml file and the output image is colored appropriately, so it would seem to be something to do with the interaction with renderd/mod_tile

Also, for what it's worth, I do not have any OSM data downloaded...though I wouldn't think that would stop it from working.

<Map srs="+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0.0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs +over" background-color="#8db0d3" maximum-extent="-20037508.34,-20037508.34,20037508.34,20037508.34">
  <Style name="DISCRETE RAINBOW">
    <Rule>
      <RasterSymbolizer>
        <RasterColorizer default-mode="discrete" default-color="yellow" >
            <stop color="red"    value = "0"  />
            <stop color="orange" value = "5"  />
            <stop color="yellow" value = "10" />
            <stop color="green"  value = "15" />
            <stop color="blue"   value = "20" />
            <stop color="indigo" value = "25" />
        </RasterColorizer>
      </RasterSymbolizer>
    </Rule>
  </Style>

  <Layer name="dataraster" srs="+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0.0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs +over">
      <StyleName>DISCRETE RAINBOW</StyleName>
      <Datasource>
          <Parameter name="file">/data/srtm/n41w073.hgt</Parameter>
          <Parameter name="type">gdal</Parameter>
          <Parameter name="band">1</Parameter>
      </Datasource>
  </Layer>

</Map>

Answer 1

In case anyone is interested, the problem above was a simple error on my part - the srs for the Layer was incorrect.