Ask any layman to think of advertising and one of the first images that will spring to mind is a big, bold billboard. There can be no denying that traditional outdoor advertising is one of the quintessential marketing mediums. It is literally the biggest form of regular media. But it is changing fast. Digital technologies and new thinking mean billboards and screens are much more high-tech, interactive and personalized than the giant hoardings of old. Anyone who has worked in the out-of-home industry for more than five years has already seen it transform almost beyond recognition. And it continues to change.