Google analyses your website and its adverts in an attempt to place them in the most appropriate locations. Its how Google makes its money so will want the maximum amount of clicks.
We can however influence the locations where your adverts will be seen. When someone looks at a website your rough location is known so we can tell Google “Display adverts in a 20 mile radius of Greenwich”.
The radius and centre of area can be chosen and tested to see what gives the best results.
The advantage of PPC is that you only pay when someone clicks on your advert and becomes a new visitor.
Tracking code can be added to your. It can then monitor the adverts to see which adverts (and the visitors they bring) actually meet specific goals.
A good goal might be they send a message from your contacts page or stay on your website for a long time. A great goal is the visitor doing something like purchasing your products or signing up to a service.
The key is to create a number of advertisements and see which one works the best and make more of those and remove the others.