  For every convex disk $K$ (a convex compact subset of the plane, with
non-void interior), the packing density $\delta(K)$ and covering density
$\vartheta(K)$ form an ordered pair of real numbers, {\em i.e.}, a point in
${\mathbb R}^2$. The set $\Omega$ consisting of points assigned this way to all
convex disks is the subject of this article. A few known inequalities on
$\delta(K)$ and $\vartheta(K)$ jointly outline a relatively small convex
polygon $P$ that contains $\Omega$, while the exact shape of $\Omega$ remains a
mystery. Here we describe explicitly a leaf-shaped convex region $\Lambda$
contained in $\Omega$ and occupying a good portion of $P$. The sets $\Omega_T$
and $\Omega_L$ of translational packing and covering densities and lattice
packing and covering densities are defined similarly, restricting the allowed
arrangements of $K$ to translated copies or lattice arrangements, respectively.
Due to affine invariance of the translative and lattice density functions, the
sets $\Omega_T$ and $\Omega_L$ are compact. Furthermore, the sets $\Omega$,
$\Omega_T$ and $\Omega_L$ contain the subsets $\Omega^\star$, $\Omega_T^\star$
and $\Omega_L^\star$ respectively, corresponding to the centrally symmetric
convex disks $K$, and our leaf $\Lambda$ is contained in each of
$\Omega^\star$, $\Omega_T^\star$ and $\Omega_L^\star$.
