In order to acquire data on current public transport usage statistics and public transport users preferences and needs, each transport authority has to carry out public transport surveys. In Cape Town, South Africa, one of the most common surveys used to collect this data are ride check surveys (Moving Ahead 2001). Ride check surveys are also considered more advantageous than other public transport surveys, which involve the distribution of questionnaires to passengers, because ride check surveys are based on the observation method of data collection. This method leads to the collection of more accurate data because it does not rely on the respondent’s willingness and ability to respond to the questions (Wermuth et al 2001).
Traditionally, during ride check surveys in Cape Town, a surveyor would board a public transport vehicle for the duration of one trip. The surveyor would manually record, at every stop, the number of people boarding or getting off the vehicle, the method of payment of the ticket for the passengers boarding the vehicle, descriptive information on the position of the stop and the stop number. This would present a problem when the vehicle stops at any place that is neither an existing stop nor a terminus. There would be no location information on that stop available in the database. Any attempts to represent such a place on a map results in an inaccurate representation because an approximate position will be used. Sometimes, when visibility is poor, the surveyor would find it difficult to read off the stop number from the stop shelter in the short time that the vehicle stops to drop off or pick up passengers. The manual recording of the arrival and departure times at each stop and the counting of the people getting on and off the vehicle would also result in inaccurate data due to human error and fatigue.
To overcome these shortfalls, some local authorities in South Africa have adopted the use of automatic positioning systems for location positioning and electronic data devices for recording the data during these surveys. It is also important to note that similar problems are being experienced in other countries and that the adoption of these devices is not only occurring in South Africa but can be seen as a worldwide phenomenon (Shaw 1999 and Murakami et al 1997). An example of the use of this technology in South Africa is the use of global positioning systems (GPS) and palm pilots by the Cape Metropolitan Council in carrying out ride check surveys in the year 2000 (AfriGIS 2000).
During these ride check surveys, a surveyor was placed on a selected bus trip, armed with a GPS receiver and a palm pilot. At every stop, the surveyor recorded the following information:
- The stop position in terms of x and y co-ordinates.
- The arrival and departure times.
- The number of passengers boarding and alighting.
- The method of payment used (whether cash or clip card).
This leads to the generation of large amounts of data, which create the need for effective methods of data organisation, representation and visualization (Goodchild 1999 and Papacostas 1995).
As most local authorities and public service providers are already using GIS for transport information management and service planning, it becomes a natural choice for storing the ride check survey data. GIS provides capabilities for graphical presentations that make analysis of the data easier (Zhong 1998, Wang et al 2001, Attanucii et al 1999). It is also the preferred output format for any current public transport record according to the South African public transport policy (Department of Transport 2001).
In most cases, any attempts to include such survey data in the GIS often leads to the data being stored in flat files. This results in databases with lots of redundancies. In order to efficiently represent this kind of data in a GIS, a suitable data model has to be designed. The following sections will discuss on the design and implementation of a suitable data model for representation of ride check survey data in a GIS.