To be honest the online advertising could be said to have the widest scope of reach; the method can reach any one on earth as long as has internet. This does not mean it is the best for there are other factors which must be put in mind. It would be useless to reach people who do not understand your product and can not be serviced if there is demand. It is like selling sand to people in the deserts.

If the numbers of people who view your outdoor advertising are specific to your product; the scope in some way can be said to be high. You can have a million viewers of your advertisement but only ten buy, but you can have an outdoor board outside your store which is viewed by a hundred people of whom fifty going and make purchases thus it would be more effective.

One of the short coming of the PPC advertising is fraud; the web publishers are paid when clicks are made from their sites thus they collude with friends to keep clicking from different IP locations so as to earn more money. So the number is high by in reality it is the same people viewing you advertisement in multiple numbers.

Radio advertising has for a long time been constrained by area or reach, but with internet streaming the problem has been solved and you can access your favorite radio channel from anywhere in the world. If your products market is local; radio can greatly assist in advertising it for most of them are regionalized.