  We derived position-velocity density distribution diagrams along the major
(PA = 77$^{\circ}$) axis of the elliptical planetary nebula NGC 7009 with the
Keck HIRES [SII] 6716/6731 \A, doublet spectral images. The average densities
of the main shell and knots of NGC 7009 derived from the [SII] 6716/673 \A,
fluxes integrated over the line of sight indicate a density range of $N_{\rm
e}$ = $10^{3.4}$ to 10$^{3.9}$ $cm^{-3}$, while the local densities from the
volume fraction resolved in radial velocities along the line of sight show a
considerably large range of about 10$^{2.8}$ -- 10$^{4.7}$ $cm^{-3}$. The
derived projection angle of the major axis of the main shell is about $\psi
\sim$18.3($\pm$2)$^{\circ}$. Assuming that the main shell is an ellipsoidal
shell with $a \simeq$16$''$ and $b \simeq 6''$, we found the range of expansion
velocity, radius, and latitude of four knots and a hot bubble. The four knots
at the points in symmetrical positions are roughly aligned with the same axis
of expansion of latitudes $\phi \sim \pm 34.5(\pm 0.6)^{\circ}$: One pair
expands at about 35 $kms^{-1}$ close to the main ellipsoidal shell, and the
other expands rapidly at about 60 $kms^{-1}$ at a distance of $r \sim 16''$. In
the latitude range $\phi = $65 -- 75$^{\circ}$, the hot bubble of a relatively
large structure expands rapidly with a velocity of 130 -- 150 $kms^{-1}$. Four
knots and hot bubble points that expand faster than the main shell appear to
have been formed by two to three eruptions at a different epoch than the
primary structure formation.
