Geoscience Reference
In-Depth Information
Betweenness measures to what extent a given road is between roads. Nor-
mally the higher the betweenness, the more important the given road is. In
a dual graph, it reflects to what extent a node is located in between the
paths that connect pairs of nodes in a network. It is defined by
n
(
i
)
1
B
i
jk
C
=
(3)
(
N
1
)(
N
2
n
j
,
k
N
;
j
k
;
k
i
jk
n
is the number of shortest paths from j to k , and
n jk
( i
)
where
is the
jk
number of shortest paths from j to k that pass through i .
2.3 Thematic properties
Thematic properties (or attributes) always exist in the database, if any. A
number of thematic properties may be used to determine the importance of
individual roads. Li and Choi (2002) investigated six different ones which
were road type (or class), length, number of lanes, number of traffic direc-
tions, width and connectivity. From our observations, in most cases, road
class is often available and other properties may be unavailable .
3- An experimental design for evaluation of various properties
Since a number of properties to determine the importance of individual
roads have been introduced, it is nature to follow up with an evaluation of
them to see which one(s) may produce better results for road network
generalization. This section will give an experimental design for evaluation.
3.1 Properties to be tested
In the experiment, five different properties which include :
one geometric property: length,
three topological properties: degree, closeness and betweenness, and
one thematic property: road class
are used for comparative testing.
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