1. A method of displaying wireless-spectrum usage information, the method comprising: monitoring wireless-spectrum usage concurrently at wireless-spectrum monitoring locations distributed over a geographic region by operation of wireless-spectrum analysis devices distributed over the geographic region; transmitting, from each wireless-spectrum analysis device, spectral-usage data identified by the wireless-spectrum analysis device analyzing physical layer signals detected at its wireless-spectrum monitoring location; aggregating the spectral-usage data transmitted from the wireless-spectrum analysis devices; generating, by operation of data processing apparatus, a surface plot of a measure of wireless-spectrum usage for the geographic region based on the aggregated spectral usage data; and superimposing, by operation of a display device, the surface plot onto a view of the geographic region, the superimposed surface plot visually indicating values for the measure of wireless-spectrum usage over the geographic region.