Geography Reference
In-Depth Information
13.4.1
Case and Sample
The field study was conducted in Guangzhou from January 11th to May 30th 2011.
Guangzhou, the capital city of Guangdong province of China and a major metropolis
in the Pearl River Delta, was chosen for our field study because of the availability of
detailed land use data, sufficient complexity of urban environment and convenience
for us to collect data. With a limited research budget and number of GPS devices,
we recruited in total 21 respondents with different socio-demographic backgrounds
such as occupation and age. The respondents participated in the survey for 325
days, resulting in a dataset of 168 person-days in which a total of 859 activities
were reported by the respondents.
13.4.2
Collection of GPS Tracking Data and Activity Dairies
As already mentioned above, GPS has been widely used because of its good perfor-
mance in providing accurate three-dimensional spatial and temporal information in
outdoor environments. Recently, cellular phone tracking based on Global System for
Mobile Communication (GSM) network has attracted attention due to the popularity
of smart phones. Although the GSM network is widespread, its positioning accuracy
is only about 50-100 m (Retscher and Kealy
2005
; Sun et al.
2009
). Despite that
some of the operating systems like Android in HTC/Google and iPhone OS in
iPhone have embedded Assisted GPS (AGPS), our test of iPhone 4 in Hong Kong
shows the accuracy varies a lot from several meters to dozens of meters in different
situations. Worse still, the use of AGPS in mobile phone greatly reduced its battery
life. On the other hand, further improvements of GPS technology in size, weight
and power supply make it more convenient for respondents to bring with wherever
they go. For the above reasons, this study chose to use the more reliable portable
GPS devices for collecting tracking data. The type of portable GPS devices (size:
90 mm
44 mm
10 mm; weight: 50 g) that we used is assisted by GSM signal and
can achieve a positioning accuracy of about 2.5 m. In total 11 devices were used.
Except that two devices were out of order due to battery problems, all the other
devices work well. An on-line monitoring system was developed by the GPS device
provider. Once the devices are turned on and begin tracking, they are highlighted
on the right panel of the system. These GPS tracking data with WGS-84 Coordinate
System can be immediately uploaded to this system and displayed on the digital
map when start and end time is provided.
As noted before, each of the participants was required to bring the above GPS
device when performing their daily activities and report all their activities and trip
making through a paper-based questionnaire for a number of days. Besides some
instructions of GPS device in the questionnaire, spaces were also left for participants
to fill in some basic data like home, school or work address, places that they
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