  Metro or transit maps, are schematic representations of transit networks to
facilitate effective route-finding. These maps are often advertised on a web
page or pamphlet highlighting routes from source to destination stations. To
visually support such route-finding, designers often distort the layout by
embedding symbolic shapes (e.g., circular routes) in order to guide readers'
attention (e.g., Moscow map and Japan railway map). However, manually producing
such maps is labor-intensive and the effect of shapes remains unclear. In this
paper, we propose an approach to generalize such mixed metro maps that take
user-defined shapes as an input. In this mixed design, lines that are used to
approximate the shapes are arranged symbolically, while the remaining lines
follow classical layout convention. A three-step algorithm, including (1)
detecting and selecting routes for shape approximation, (2) shape and layout
deformation, and (3) aligning lines on a grid, is integrated to guarantee good
visual quality. Our contribution lies in the definition of the mixed metro map
problem and the formulation of design criteria so that the problem can be
resolved systematically using the optimization paradigm. Finally, we evaluate
the performance of our approach and perform a user study to test if the
embedded shapes are recognizable or reduce the map quality.
