Geoscience Reference
In-Depth Information
negative correlation between distance and the importance of the interrelation
between a given pair of nodes. Although a large body of literature exists which is
dedicated to different types of distance decay functions [
26
,
27
], we decided to
restrict the tests of our methodology to only one of those most commonly used in
accessibility studies: the negative exponential function ([
12
,
28
,
29
], among others):
f
ð
c
ij
Þ¼
exp
ð
b
c
ij
Þ
ð
2
Þ
parameter allows one to estimate the
accessibility level in terms of different travel purposes [
13
]. We chose time as a
distance decay element. As the methodology presented is potentially valuable for
the local scale of analysis, we decided to select the
The selection of a particular value of
β
parameter of 0.023105, which
corresponds to short-distance trips (e.g. commuting), i.e. median travel time is equal
to 30 min [
23
]. The assumed median travel time is in accordance with empirical
observations derived from the Warsaw Traffic Survey [
30
].
Taking this further, the incorporation of self-potential is an important factor that
leads to the obtaining of proper values of the potential accessibility indicator [
31
,
32
]. The calculation of self-potential is based on the estimation of internal travel
time within a given spatial unit that is based on the radius ri,
i
, involving the formula
proposed by Rich [
33
]:
β
0
:
5
r
i
v
ii
t
ii
¼
ð
3
Þ
using a speed vii
ii
equal to 20 km/h as the assumed internal travel time. Similarly, the
travel time between each pair of nodes should be increased to take account of the
time needed to arrive at the origin and destination node (access and egress time).
This is achieved by the application of the same formula as that used for obtaining the
internal travel time (separately for both origin and destination units respectively).
3 Study Area and Data Processing
The proposed methodology has been tested on the Mazovia region, the biggest
(35,600 km
2
) and the most populated (5.2 m inhabitants) voivodeship (NUTS-2
unit) in Poland. This region is strongly monocentric, with the dominant role of the
capital city, Warsaw, and its metropolitan area. However, it is also highly diverse in
terms of population density and settlement structure, as well as in terms of density
and the quality of road transport networks. The motorway network is unequally
distributed and consists of a relatively well-developed infrastructure in the south-
western part of the region, and only a few, short and fragmented motorway sections
in the eastern and northern parts of Mazovia.
Apart from its internal diversity, themost signi
cant characteristic of the study area
is its central location in Poland. In spatial analysis, distortion of the results can be
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