  Resonances are uniquely characterized by their complex pole locations and the
corresponding residues. In practice, however, resonances are typically
identified experimentally as structures in invariant mass distributions, with
branching fractions of resonances determined as ratios of count rates. To make
contact between these quantities it is necessary to connect line shapes and
resonance parameters. In this work we propose such a connection and illustrate
the formalism with detailed studies of the $\rho(770)$ and $f_0(500)$
resonances. Based on the line shapes inferred from the resonance parameters
along these lines, expressions for partial widths and branching ratios are
derived and compared to other approaches in the literature.
