Measuring the audience to poster advertising

Since the early 1950s the medium has moved from having no audience research whatsoever tu the present complex of methods and models. As with press or television, a means of estimating the cover and frequency delivered by any given campaign is vital. Additionally, those who own it need to be able to determine the value of the individual units they are selling. How many peop le pass each site in vehicles or on foot, who are they, and how easily can they see the advertisements displayed? It has not proved easy to supply com pletely satisfactory answers to these questions, but gains in computing, in statistical method and in technology have now brought the research systems to an advanced state of development.