If you are worried about not showing in another area you can always check if you will be, by selecting that city in your campaign settings search. If you notice Boulder and Broomfield do not have any areas that are in common, so you would not have to exclude anything. However Broomfield and Denver do have some common area and there is the potential that you could show in the other area.
If your campaign is showing in a city you don’t want it to you can exclude the city by using negative keywords. In this map we selected 3 areas (Boulder, Broomfield and Denver). As you can see the area Google uses for the cities is not exact so you may have to exclude cities you don’t’ want to show up in. For example if you only wanted to show in Denver but not Broomfield you would want to exclude it. For every ad group within the campaign for the Denver area you will want to add a negative keyword, you can do this simply by selecting add keywords and before the keyword using the – symbol. For the example they would want to use the keyword –Broomfield. By doing this your ad will not show in their area when they are searching for a generic term like carpet cleaning, however if they were to search for carpet cleaning Denver from that area you would still show up.