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", "contour4a")  ; Open a PS file called "contour4a.ps"

  res = True                             ; No plot options desired.

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