Table 1.

Categories of concepts related to vertex-edge graphs

Concepts related to vertex-edge graphs	Description
Edges	This category includes all codes in which students look more closely at the edges of the vertex-edge graph (not the nodes)
Metrics	This code is assigned to the weighting of road sections. This may be the length of a road or the presence of traffic lights or roadworks, etc., for which these roads should be avoided if possible (or at least should not be covered twice)
Effectiveness: Duplications	Consideration of roads covered twice
Effectiveness: Omissions	Consideration of omitted roads
Cover	Proportion of road coverage by the vertex-edge graph
Vertex-edge graph structure	This category includes all codes in which students look more closely at the structure of the vertex-edge graph
Subgraph	Considerations for viewing a sub-graph
Graph complexity	Development of basic insights into which a Euler graph might be created become apparent
Duplicates	Considerations of road sections covered twice, whereby the double driving is explicitly not done for reasons of time or path saving (for example, because in reality it seems easier to turn right instead of turning left)
Start and end points	Considerations of where the start and end points should be; also considerations of tour or circle
Directed graph	Concrete: Consideration of one-way street
Passage sense	Consideration of whether the graph should be covered from A to B or from B to A (e.g. because of left turns)
Generalisation	Discussion of transferring the model to other city districts or to other real situations