5. Concluding remarks
Estimation of travel time between a set of origins and a
set of destinations through a transportation network is a
common task in spatial analysis. Calibrating the O–D travel
time matrix in a commercial GIS package requires extensive
data collection and processing to prepare the road
network and also adequate knowledge of the software to
implement related tools. Both are no trivial efforts. This
research has developed a desktop tool to complete the
task by calling the Google Maps API. The Python program
automates the process by reading the layers of origins
and destinations in geographic coordinates, executing a
HTTP request to access the Google Maps and calibrate the travel time between each O–D pair, and saving the results
in an external ASCII file. By comparing the approach
with the commonly used ArcGIS Network Analyst module,
several advantages are identified: no need of preparing
a road network, using a more updated road network, and
accounting for congestion in high-traffic areas and peak
hours. Our case study in accessibility analysis indicates that
an accurate estimate of travel time is essential in spatial
analysis.
The GoogleMaps API approach is not free of concerns.
Our experiments have revealed some limitations. First of
all, an ordinary user without a paid license to Google Maps
API Premier is subject to a daily query limit of 2500 geolocation
requests and is likely to experience some ‘hiccups’
in executing the tool. We welcome feedbacks from users
with a Google Maps API Premier license. Second, all data
used in the computation are maintained by Google, and
thus a user has neither control over its quality nor any
editing rights. While the Google’s road network has a reputation
of good quality, no data are completely free of errors.
Most users may not care about any modification rights of
network data, but the lack of data transparency is nevertheless
a drawback for many advanced researchers in spatial
analysis. Furthermore, the tool can only generate the contemporary
travel time by accessing the most updated road
network data in Google. In some cases, researchers need
the travel time in the past. Such a task is only feasible by
using a historical road network. Finally, the tool is currently
implemented in a desktop GIS environment. It is our plan
to develop an online version in the near future.
5. Concluding remarks
Estimation of travel time between a set of origins and a
set of destinations through a transportation network is a
common task in spatial analysis. Calibrating the O–D travel
time matrix in a commercial GIS package requires extensive
data collection and processing to prepare the road
network and also adequate knowledge of the software to
implement related tools. Both are no trivial efforts. This
research has developed a desktop tool to complete the
task by calling the Google Maps API. The Python program
automates the process by reading the layers of origins
and destinations in geographic coordinates, executing a
HTTP request to access the Google Maps and calibrate the travel time between each O–D pair, and saving the results
in an external ASCII file. By comparing the approach
with the commonly used ArcGIS Network Analyst module,
several advantages are identified: no need of preparing
a road network, using a more updated road network, and
accounting for congestion in high-traffic areas and peak
hours. Our case study in accessibility analysis indicates that
an accurate estimate of travel time is essential in spatial
analysis.
The GoogleMaps API approach is not free of concerns.
Our experiments have revealed some limitations. First of
all, an ordinary user without a paid license to Google Maps
API Premier is subject to a daily query limit of 2500 geolocation
requests and is likely to experience some ‘hiccups’
in executing the tool. We welcome feedbacks from users
with a Google Maps API Premier license. Second, all data
used in the computation are maintained by Google, and
thus a user has neither control over its quality nor any
editing rights. While the Google’s road network has a reputation
of good quality, no data are completely free of errors.
Most users may not care about any modification rights of
network data, but the lack of data transparency is nevertheless
a drawback for many advanced researchers in spatial
analysis. Furthermore, the tool can only generate the contemporary
travel time by accessing the most updated road
network data in Google. In some cases, researchers need
the travel time in the past. Such a task is only feasible by
using a historical road network. Finally, the tool is currently
implemented in a desktop GIS environment. It is our plan
to develop an online version in the near future.
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