# Betweenness / Directed betweenness

Betweenness is a graph centrality measure that shows how often a domain appears on the shortest path between any given pair of domains (see Distance for more about paths). Betweenness is calculated using the graph of links relationships for the ecosystem. Directed betweenness is calculated using the graph of backlinks referral relationships for the ecosystem.

Domains with relatively high Betweenness or Directed betweenness scores may bridge different parts of
the network, and can be useful to evaluate as candidates to approach for backlinks (when not
**principal** or **competitor** domains).

A nice way to understand betweenness is road junctions in a city. Ask a taxi driver to draw on a map the shortest routes between every possible pairing from a list of 100 hotels in the city. Some junctions will feature on these routes much more frequently than others - these are junctions with higher betweenness scores, because they are more often on the shortest route between each pairing.

## Calculating Betweenness

Betweenness scores are on a scale from 0 to 1.

In the following illustration, domain A has links relationships with all the X and Y domains:

The shortest path between any of the X domains and any of the Y domains will always pass through domain A. For example, the shortest path between domain X1 and Y3 passes through domain A:

In this mini-ecosystem, domain A will have a high Betweenness score (in fact, it will have the highest Betweenness score).

## Calculating Directed betweenness

Directed betweenness scores are on a scale from 0 to 1.

In the following illustration, domains A and B are connected by backlinks referral relationships to some of the X and Y domains:

To calculate Directed betweenness, paths must follow the direction of the relationships. In the following illustration, the shortest path between domain Y3 and X2 follows the direction of the relationships, and passes through domain B:

However, domain A only has relationships *from* it *to* other domains. No paths that follow the
direction of relationships between other pairs of domains will ever pass through domain A:

In this mini-ecosystem, domain B will have a higher Directed betweenness score, and domain A will have a zero score.

## Visualising Betweenness / Directed betweenness

In the main visualisation of a report interactive, the
'Betweenness', and 'Directed betweenness' views re-colour the domains to indicate their respective values. This
re-colouring is relative, not absolute, so 'High' means high in the context of this ecosystem,
and excludes **principal** and **competitor** domains.

## Viewing Betweenness / Directed betweenness values

All worksheets in the MS Excel file for a report that list domains contain
`Betweenness (lr)`

, and `Directed betweenness (br)`

columns for these
attributes. The `(lr)`

and `(br)`

at the end of each column name denotes
whether the value is calculated using the graph of links relationships, or the graph of backlinks referral
relationships.