请教坐标的问题

濤爺

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

  in = addfile("/media/lht/lht/data/u.nc","r")
     u = in->u(18,::-1,::-1,:)
     uflt = short2flt(u)   
     uAvgLon = dim_avg_n( uflt, 2 )
     uAvgLon!0="pre"
     uAvgLon!1="lon"
     uAvgLon&pre=(/1000,975,950,925,900,875,850,825,800,775,750,700,650,600,550,500,450,400,350,300,250,225,200,175,150,125,100,70,50,30,20,10,7,5,3,2,1/)
uAvgLon&lon=fspan(-90.,90.,241)
     printVarSummary(uAvgLon)   
wks = gsn_open_wks("ps" ,"picture0")     

  plot = gsn_contour(wks,uAvgLon, False)



end

我用的是nc数据，画出来的图怎么是格点坐标，比如纬度应该是90S到90N,但是我画出来的图横坐标却是0到240（因为0.75*0.75的数据）