Geoscience Reference
In-Depth Information
Harrie 2004) In practice, a road network in the database is often repre-
sented by single lines, especially at middle or small scale dataset. There-
fore, length is more widely used than width. Normally the longer the road
length, the more important the road is.
2.2 Topological properties
A series of topological properties has been proposed to detect network
characteristics. Degree, closeness and betweenness are just three of them
and they can be used to determine the important nodes or links within the
network such as social network (Freeman 1979), street network (Jiang and
Claramunt 2004; Crucitti et al. 2006) and so forth. In the road network, in
order to calculate the importance of individual road, it is needed to repre-
sent the road network as a dual graph in which individual roads are taken
as nodes and road intersections are taken as links (Porta et al. 2006). And
the importance of each road can be respectively calculated according to
three properties as follows (Jiang and Harrie 2004):
Degree
measures the number of roads that interconnect a given road.
Normally the higher the degree, the more important the given road is. In a
dual graph, degree is the number of nodes that link a given node. Formally,
the degree centrality for a given node
i
is defined by:
∈
D
i
C
=
a
(1)
ij
j
N
where
N
is the total number of nodes in the graph,
i
a
is 1 if there is
a link between node
i
and node
j
, and 0 otherwise.
Closeness
measures the smallest number of links from a given road to all
other roads. Normally the higher the closeness, the more important the
given road is. In a dual graph, it is the shortest distance from a given node
to all other nodes. It is defined by:
N
−
1
C
i
(2)
C
=
∑
≠
d
ij
j
∈
N
,
j
i
where
d
is the shortest path length between
i
and
j
.
ij
