  The concept of a \emph{weak value} of a quantum observable was developed in
the late 1980s by Aharonov and colleagues to characterize the value of an
observable for a quantum system in the time interval between two projective
measurements. Curiously, these values often lie outside the eigenspectrum of
the observable, and can even be complex-valued. Nevertheless, the weak value of
a quantum observable has been shown to be a valuable resource in quantum
metrology, and has received recent attention in foundational aspects of quantum
mechanics. This paper is driven by a desire to more fully understand the
underlying mathematical structure of weak values. In order to do this, we allow
an observable to be \emph{any} Hermitian operator, and use the pre- and
post-selected states to develop well-defined linear maps between the Hermitian
operators and their corresponding weak values. We may then use the inherent
Euclidean structure on Hermitian space to geometrically decompose a weak value
of an observable. In the case in which the quantum systems are qubits, we
provide a full geometric characterization of weak values.
