Another way of depicting these situations is by the graph in Fig. 1.4. Here we have
removed the 'crossing' of the lines PS and QT by drawing the line PS outside the rectangle
PQST. The resulting graph still tells us whether there is a direct road from one
intersection to another, how the electrical network is wired up, and which football
teams have played which. The only information we have lost concerns 'metrical' properties,
such as the length of a road and the straightness of a wire.