All sorts of wireless devices, from smart phones to weather sensors, transmit data using electromagnetic signals. In order for these devices not to interfere with one another, the frequencies on which different kinds of devices communicate are carefully delineated; in practice, there is only a finite range of frequencies (known as spectrum) available, so new application developers need to know what frequencies are still on offer in their areas.
The Google Spectrum Database, which opened freely to developers last week, helps solve this problem, mapping the empty spaces in the portion of the spectrum previously reserved for TV stations. This helps enable applications that would use this spectrum to serve Wi-Fi, ultimately helping provide wireless internet to rural and other underserved areas. The database offers an API, as well as raw data for download in the common CSV format.