load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl" 
load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_csm.ncl"   

begin
  a       = addfile("pop.nc","r")     ; Read in POP data.
  t       = a->t
  t@lat2d = a->lat2d
  t@lon2d = a->lon2d

  wks = gsn_open_wks("ps", "contour4d")    ; Open PS file called "contour4d.ps"

  gsn_define_colormap(wks,"BlAqGrYeOrRe")  ; Choose color map

  res                 = True
  res@gsnAddCyclic    = True               ; Add cyclic point.
  res@cnFillOn        = True               ; Turn on contour fill.
  res@cnFillMode      = "RasterFill"       ; Turn on raster fill.
  res@gsnSpreadColors = True               ; Span color map.

  plot = gsn_csm_contour_map(wks,t,res)    ; Call the gsn_csm function for
                                           ; drawing contours over a map.
end