Beyond Space (As We Knew It): Toward Temporally Integrated Geographies of Segregation, Health, and Accessibility - Space-Time Integration in Geography and GIScience - page 44

They also ignore the fact that people move around to undertake their daily routines
and as a result may be presented with various opportunities for accessing needed
material and emotional resources and improving their quality of life (Takahashi
et al. 2001 ).
In many senses, time is a fundamental dimension that shapes people's access
to and use of urban opportunities. Individuals have different space-time constraints
and temporal rhythms of activities throughout the day (Kwan 1998 , 1999 ; Dijst and
Vidakovic 2000 ;Schwanenetal. 2008 ;Farberetal. 2013 ). These constraints and
temporal rhythms may also vary considerably from day to day (Neutens et al.
2010 ). Facilities and services have specific temporal schedules or opening hours
that render them unavailable in certain hours of the day, and individual accessibility
of people with different personal and household attributes can be affected differently
by changes in these opening hours (Neutens et al. 2010 ; Delafontaine et al. 2011 ).
Further, not all opportunities are relevant unless the time one can spend at the
activity site exceeds the threshold requires for meaningful participation in that
activity (Kim and Kwan 2003 ). Various types of delays people encountered during
their travel, such as traffic congestion or changes in transit schedules in different
hours of the day, also affect the extent to which facilities can be accessed or used
(Weber and Kwan 2002 ).
Simply put, locational proximity does not necessarily mean better access for
many people. For instance, a government office is not necessarily very accessible
even if it is located right next to a person's residence if the person's space-time
constraints (e.g., work schedule) make it difficult to visit the office during its
opening hours. Public transit is not necessarily accessible even if one lives right
next to a bus stop if the bus schedule does not entail frequent service at the time it is
most needed. Ignoring people's space-time constraints and the temporal schedules
of facilities or services can lead to serious overestimation of the level of access
people actually experience.
While only a few studies to date have compared results obtained from including
and ignoring the temporal dimension in accessibility research, they provide strong
evidence about the possibility of erroneous conclusions when time is ignored. For
instance, Kwan ( 1998 ) compares 18 conventional accessibility measures with 12
space-time measures that take into account people's space-time constraints and the
sequential unfolding of their activities over time. The study found considerable
gender differences in the geographic patterns of accessibility when using space-
time measures, while no such differences were observed when using conventional
measures. This result means that accessibility measures that do not take time and
human mobility into account may not reveal the effects of social difference (e.g.,
gender, race, class, age, and disability) on individual accessibility because they are
not sensitive to people's space-time constraints.
More recently, Ren et al. ( 2014 ) compare the geographic patterns of demand
for service generated with three conventional location-based demand measures and
eight demand measures that take into account people's space-time accessibility.
The study found that ignoring the temporal dimension of accessibility in demand
modeling may underestimate potential demand for service in most situations and