This layouttries to optimise the placement of nodes so that they adhere to the classic look of metro maps. As such it optimizes on the distribution of incident edge angles, conformity of edge length, and edge angles in multiples of 45 degrees. As it works as a refinement of an already existing layout (the physical location of metro stations) it requires an a priori node location. Due to it's purpose it probably works best with planar graphs.

layout_tbl_graph_metro(
graph,
x,
y,
length = 2,
grid_space = 0.0025,
optimization_weights = NULL,
max_movement = 5,
circular = FALSE
)

## Arguments

graph

A tbl_graph object

x, y

The start location of the nodes

length

Desired multiple of grid point spacing. (length * grid_space determines desired edge length)

grid_space

The distance between consecitive grid points

optimization_weights

The relative weight to be placed on the 5 criteria during optimization as a numeric vector of length 4. The criteria are:

• Angular Resolution Criterion: The angles of incident edges at each station should be maximized, because if there is only a small angle between any two adjacent edges, then it can become difficult to distinguish between them.

• Edge Length Criterion: The edge lengths across the whole map should be approximately equal to ensure regular spacing between stations. It is based on the preferred multiple, l, of the grid spacing, g. The purpose of the criterion is to penalize edges that are longer than or shorter than lg.

• Balanced Edge Length Criterion: The length of edges incident to a particular station should be similar.

• Line Straightness Criterion: (not yet implemented) Edges that form part of a line should, where possible, be co-linear either side of each station that the line passes through.

• Octiinearity Criterion: Each edge should be drawn horizontally, vertically, or diagonally at 45 degree, so we penalize edges that are not at a desired angle. If NULL all criteria are given equal weight.

max_movement

Number of grid points a station can move away rom its original position

circular

ignored

## Value

A data.frame with the columns x, y, circular as well as any information stored as node variables in the tbl_graph object.

## References

Stott, J., Rodgers, P., Martinez-Ovando, J. C., and Walker, S. G. (2011). Automatic metro map layout using multicriteria optimization In IEEE Trans Vis Comput Graph 17(1) pp. 101-114. https://doi.org/10.1109/tvcg.2010.24

Other layout_tbl_graph_*: layout_tbl_graph_auto(), layout_tbl_graph_backbone(), layout_tbl_graph_cactustree(), layout_tbl_graph_centrality(), layout_tbl_graph_circlepack(), layout_tbl_graph_dendrogram(), layout_tbl_graph_eigen(), layout_tbl_graph_fabric(), layout_tbl_graph_focus(), layout_tbl_graph_hive(), layout_tbl_graph_htree(), layout_tbl_graph_igraph(), layout_tbl_graph_linear(), layout_tbl_graph_manual(), layout_tbl_graph_matrix(), layout_tbl_graph_partition(), layout_tbl_graph_pmds(), layout_tbl_graph_sf(), layout_tbl_graph_stress(), layout_tbl_graph_treemap(), layout_tbl_graph_unrooted()