PLANAR_CODE is the most common encoding for planar graphs, and is supported by various generation and visualisation tools. It is a binary format and not intended to be human-readable.
The default encoding only supports graphs with
<256 nodes, and
2*|E|+|N|+1 bytes per graph.
Please note that PLANAR_CODE is not suitable for graphs with multiple loops on vertices (multiple edges with distinct endpoints however are catered for). As such, no guarantees are made about what happens with multiple loops.