# Transportation Geography and Network Science/Characterizing Graphs

## beta indexEdit

The beta index ($\beta$) measures the connectivity relating the number of edges to the number of nodes. It is given as:

$\beta=\frac{e}{v}$

where e = number of edges (links), v = number of vertices (nodes)

The greater the value of $\beta$, the greater the connectivity. As transport networks develop and become more efficient, the value of $\beta$ should rise.

## cyclomatic numberEdit

The cyclomatic number ($u$) is the maximum number of independent cycles in a graph.

$u=e-v+p$

where p = number of graphs or subgraphs.

## alpha indexEdit

The alpha index ($\alpha$) is the ratio of the actual number of circuits in a network to the maximum possible number of circuits in that network. It is given as:

$\alpha=\frac{u}{2v-5}$

Values range from 0%—no circuits—to 100%—a completely interconnected network.

## gamma indexEdit

The gamma index ($\gamma$) measures the connectivity in a network. It is a measure of the ratio of the number of edges in a network to the maximum number possible in a planar network ($3(v-2)$)

$\gamma=\frac{e}{3(v-2)}$

The index ranges from 0 (no connections between nodes) to 1.0 (the maximum number of connections, with direct links between all the nodes).

## CompletenessEdit

The number of links in a real world network is typically less than the maximum number of links and the completeness index used here captures this difference. This measure is estimated at the metropolitan level.

$\rho_{complete} = \frac{e}{e_{max}} = \frac{e}{{v^2}-{v}}$

$e$ refers to the number of links or street segments in the network and $v$ refers to the number of intersections or nodes in the network. Compare with the $\gamma$ index above.

## König numberEdit

The König number (or associated number) is the number of edges from any node in a network to the furthest node from it. This is a topological measure of distance, in edges rather than in kilometres. A low associated number indicates a high degree of connectivity; the lower the König number, the greater the Centrality of that node.

## eta indexEdit

The eta index ($\eta$) measure the length of the graph over the number of edges.

$\eta=\frac{L(G)}{e}$

## theta indexEdit

The theta index ($\theta$) measure the traffic (Q(G)) per vertex.

$\theta=\frac{Q(G)}{v}$

## iota indexEdit

The iota index ($\iota$) measures the ratio between the length of its network and its weighted vertices.

$\iota=\frac{L(G)}{W(G)}$

$W(G)=1,\forall o=1$

$W(G)=\sum_{e}2*o,\forall o>1$

Source: [1]