# Topic map diameter

Topic map diameter tells how many links need to be followed to be able to reach any topic in the topic map from any other topic. It is the same as a diameter of a graph when you treat each topic as a node and each association as an edge in the graph. Topic map diameter is measured selecting **Layers > Statistics > Topic map diameter**.

Note that the graph might not be connected, that is, there is at least one pair of topics where you cannot reach one from the other by following associations. In this case the tool used to calculate topic map diameter gives the greatest diameter of the connected componets in the topic map.

## Formal definition

Graph diameter is the maximum of minimum distances between all node pairs in the graph. Distance here means the number of edges that need to be followed in the graph to reach one node from another. Minimum distance means the shortest such path, it is common for there to be several different paths from one node to another.

For example, consider the following graph.

Minimum distance between topics 9 and 0 is 3. Starting from topic 9 go to topic 12, then topic 11 and then topic 0. The diameter of the graph is 5. There are two topic pairs with minimum distance of 5, topics 1 and topic 3, and topics 9 and 3. There are no topics that would have a greater minimum distance than 5.