The complexity of graph data visualization

In order for us to understand why graph visualization is so challenging, we are first going to investigate the easiest networks that can be visualized: physical networks.

Physical networks

By physical networks, I mean networks whose nodes (and sometimes edges) have fixed spatial positions (coordinates). That includes the following:

• Road networks: Street intersections (nodes) have spatial coordinates (latitude and longitude). Edges (the roads themselves) also have a shape or geometry (linestring) that can be stored using a geospatial data format (shapefile or GeoJSON, for instance) and drawn on a map.
• Public transport networks: Nodes are bus/train stops with defined positions; edges are the bus paths between these stops.
• Electric network: We can imagine this as containing nodes with different types (power station, transformer, consumer, etc.). Each of them also has a precise location, and the distance between them can...