Geoscience Reference
In-Depth Information
The difference between the two homebuyer strategies—distance-only and
distance-plus-direction—lies in the probability assigned to vacant houses,
P
ij
,or
the possibility of
B
i
buying vacant house
H
j
(Fig.
6.1
). With the distance-only
strategy, each actor agent calculates
P
ij
based on the distance between her current
dwelling and a vacant house, where the probability follows a negative exponential
distribution. Assuming homebuyer
B
i
currently lives in
H
i
, the probability that she
chooses house
H
j
would be
D
e
d
.
H
i
;H
j
/
P
ij
(6.3)
where is a parameter estimated empirically from move distance distribution
(more on this below) and
d
(
H
i
,
H
j
) is the distance between
H
i
and
H
j
. With the
distance-plus-direction strategy, directional bias is also included in the calculation
of probability
P
ij
. When relocation is constrained by real housing opportunities, it
can be assumed that move direction is independent from move distance (Adams
1969
;ClarkandBurt
1980
; Clark et al.
2003
). The von Mises distribution
is modeled as two normal distributions with zero and 180
ı
as mean values,
respectively:
D
e
d
.
H
i
;H
j
/
P
P
ij
(6.4)
where
P
is the probability that a homebuyer moves in the direction of .Ifwe
1;
if
j
j
90
,then
P
D
Sign( )
N
(0,
1
)
C
[1
Sign( )]
N
(180,
2
), in which
N
(,
2
) is normal distribution. When Sign( ) is one, home-
buyers move toward the suburbs; when it is zero, they move toward downtown.
The standard deviation
1
and
2
control the extent to which migrant household
moves concentrate along the home-downtown corridor. When these deviations are
small, houses near the corridor are more likely to be chosen, but when they are
large, more houses have greater odds of being chosen. When
1
is greater than
2
,
households are more likely to move to suburbs; when smaller, households move
toward downtown.
define Sign . /
D
0;
if
j
j
>90
6.3
Methods
A key methodological challenge in understanding intraurban migration is devel-
oping straightforward, empirically specified approaches to model how the choices
of individuals generate aggregate migration patterns and processes. The primary
form of intraurban migration modeling is mathematical and statistical, ranging from
gravity modeling to hedonic specifications to various flavors of (new) economic
geography of urban areas. Less common but long-standing is simulation modeling,
which has enjoyed renewed interest in the form of agent-based modeling (ABM).
We develop an ABM of urban intramigration and use a new form of data to calibrate
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