  Radio maps characterize quantities of interest in radio communication
environments, such as the received signal strength and channel attenuation, at
every point of a geographical region. Radio map estimation typically entails
interpolative inference based on spatially distributed measurements. In this
tutorial article, after presenting some representative applications of radio
maps, the most prominent radio map estimation methods are discussed. Starting
from simple regression, the exposition gradually delves into more sophisticated
algorithms, eventually touching upon state-of-the-art techniques. To gain
insight into this versatile toolkit, illustrative toy examples will also be
presented.
