// Import some libraries and operations we'll use
  import geotrellis._
  import geotrellis.source._

  // Set up the rasters and weights we'll use:
  val r1 = RasterSource("rasterOne") // raster defined in catalog
  val r2 = RasterSource("rasterTwo")

  // This will define a RasterSource that is dthe addition of the
  // first raster with each cell multiplied
  // by 5, and the second raster with each cell multiplied by 2.
  // To understand what it means for a raster to be multiplied by an integer or
  // for two rasters to be added, see Map Algebra documentation,
  // GeoTrellis documentation or ask the mailing list/IRC.
  val added  = (r1*5) + (r2*2)

  // This divides the raster by the total weight,
  // which will give us the the final Weighted Overlay
  // (also called a Suitability Map).
  val weightedOverlay = added / (5+2)

  // Now we want to render this Weighted Overlay
  // as part of a WMS service. We could run the
  // renderPng operation with the default color ramp
  // (which is a Blue to Red color ramp descriped
  // at http://geotrellis.github.io/overviews/rendering.html).
  val rendered = weightedOverlay.renderPng

  // At this point we've only describe the work that
  // we wish to be done. Once we call 'run' on the souce,
  // we will invoke the chain of commands that we have been
  // building up, from loading the rasters from disk to
  // rendering the PNG of the wieghted overlay.

  rendered.run match {
    process.Complete(png, history) =>
      // return the PNG as an Array of Bytes
      // for spray:
      respondWithMediaType(MediaTypes.`image/png`) {
        complete { png }
      }
    process.Failure(message, history) =>
      // handle the failure.
      // for spray:
      failWith { new RuntimeException(message) }
  }