  We study the asymptotic quantization error of order $r$ for Markov-type
measures $\mu$ on a class of ratio-specified graph directed fractals. We show
that the quantization dimension of $\mu$ exists and determine its exact value
$s_{r}$ in terms of spectral radius of a related matrix. We prove that the
$s_{r}$-dimensional lower quantization coefficient of $\mu$ is always positive.
Moreover, inspired by Mauldin-Williams's work on the Hausdorff measure of graph
directed fractals, we establish a necessary and sufficient condition for the
$s_{r}$-dimensional upper quantization coefficient of $\mu$ to be finite.
