A suitable spectrum policy is essential to allow efficient use of the radio spectrum. The Japanese government currently employs a Command and Control (C&C) regime, but measures must be taken to speed up governmental decisions. The first step is to obtain spectrum utilization data which can form the basis of such decisions. This paper describes the design, implementation and evaluation of a distributed spectrum sensing system that continually measures spectrum utilization at multiple locations. The system has an architecture that enables it to utilize a wide range of existing wireless devices and measurement equipment, which can be used as sensing nodes to rapidly expand the coverage area. By focusing on the way to easily expand the measurement coverage, our work complements previous spectrum measurements, which have been conducted with high accuracy in the context of cognitive radios.