subroutine areacalc(i,npts,jxarray,jyarray,iarea)
c	sequence number of polygon
	integer i
c	no of pts in polygon
	integer npts
c	point array for all polygons
	integer jxarray(2200,900), jyarray(2200,900)
c	2*area of polygon
	integer iarea

c	point arrays for one polygon
        integer jx(900),jy(900)

c	2*area of this polygon
	iarea = 0

 	do 1722 ii=npts,1,-1

c	ii minus one
	iim1 = ii-1
	if (ii.eq.1) then
		iim1=npts
	endif

	jx(ii)=jxarray(i,ii)
	jy(ii)=jyarray(i,ii)
	jx(iim1)=jxarray(i,iim1)
	jy(iim1)=jyarray(i,iim1)

c twice area (integer)
	iarea = iarea - jx(ii)*jy(iim1) + jx(iim1)*jy(ii)

c	end of point loop ii
1722	continue

	return
	end