When we drive a car, we often want to know the circumstances of roads between the current location and the destination. Ishihara et al. proposed a Vehicular ad-hoc NETworks (VANET) -based information sharing system, called the Real-Time Visual Car Navigation System, in which a driver can obtain Location-Dependent Information (LDI), such as photographs or videos of his/her Point of Interest (PoI), by telling the onboard device, e.g., a car navigation device, the PoI. The simplest way to provide

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... DI to vehicles is to flood the LDI to all vehicles, but unneeded LDI may be disseminated, and network resources may be wasted. To disseminate LDI to many vehicles that demand it with low communication traffic, we have proposed a data dissemination scheme based on Demand maps (Dmaps). In this scheme, each vehicle has a Dmap, a data set representing the geographical distribution of the strength of demands for LDI. To keep the Dmap up to date, each vehicle exchanges a subset of data constituting a Dmap (Dmap Information: DMI) with other vehicles. Vehicles preferentially send new LDI or forwarded LDI strongly demanded to the area where the LDI is frequently demanded based on Dmaps. If vehicles frequently send DMI, the accuracy of the Dmap becomes high, however, communication traffic becomes large. In this paper, we propose strategies for controlling the frequency of sending DMI and strategies for selecting DMI to be sent to improve the Dmap accuracy with low communication traffic. Simulation results show that one of the proposed strategies, the LDI Transfer Zone (LTZ) strategy, achieves highly accurate Dmaps with a small amount of communication traffic.