Sensors can measure air quality, traffic congestion, and other aspects of urban environments. The fine-grained diagnostic information they provide could help urban managers to monitor a city’s health. Recently, a “drive-by” paradigm has been proposed in which sensors are deployed on third-party vehicles, enabling wide coverage at low cost. Research on drive-by sensing has mostly focused on sensor engineering, but a key question remains unexplored: How many vehicles would be required to adequately scan a city? Here, we address this question by analyzing the sensing power of a taxi fleet. Taxis, being numerous in cities, are natural hosts for the sensors. Using a ball-in-bin model in tandem with a simple model of taxi movements, we analytically determine the fraction of a city’s street network sensed by a fleet of taxis during a day. Our results agree with taxi data obtained from nine major cities and reveal that a remarkably small number of taxis can scan a large number of streets. This finding appears to be universal, indicating its applicability to cities beyond those analyzed here. Moreover, because taxis’ motion combines randomness and regularity (passengers’ destinations being random, but the routes to them being deterministic), the spreading properties of taxi fleets are unusual; in stark contrast to random walks, the stationary densities of our taxi model obey Zipf’s law, consistent with empirical taxi data. Our results have direct utility for town councilors, smart-city designers, and other urban decision makers.
Abstract. Even though Semantic Web technologies have flourished consistently in the past few years, it is unlikely to achieve the Semantic Web goals on the global Web in near future. The initial expectations such as turning the World Wide Web to a machine-comprehendible medium are far away from realization. The best proof of this is a look at the current status of World Wide Web and small percentage of websites and services that are Semanticallyenabled. The main reason for this situation is that so far it is not easy to get people to learn and apply Semantic Web concepts for their Web content and use them efficiently in their daily life. In this context advanced IT concepts such as Mashups can support Semantic Web goals and at the same time Semantic Web technologies can also improve computer-to-computer and human-to-computer interactions in enterprise systems. In this paper the two-way support of advanced IT and Semantic Web is explored and a novel approach for advancing the power of web forms is presented.
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