There are ways to use Google Adwords with local advertising and local traffic. With the new map roll (geo targeting) out for Google Adwords, there are somethings that I kinda missed from the old version of Adwords. Especially when it comes to geo targeting an area. With the new geo targeting interface, you enter a city and it will target that area. BUT it will also leave out less dense populated cities around or within your targeted area.
For example here is a screenshot of all the cities Google says there is reach, from county in New Jersey.
Now there maybe some good traffic which can be captured. Even though Google Adwords can not tell the populate or reach of the area doesn't mean there isn't traffic there. Granted Google may pull their location for ads being searched in their location doesn't mean it will always be covered.
To properly cover all these 'empty' areas is to create a radial target. Zoom in the map and decide what city you want as a center axis and enter it in Google's geo targeting tool, hit enter. It does not matter if the city you use as a center point is already targeted, you just need an axis for your circle. The default is a 20 mile radius, but you can go as low as 10 miles. Once you do that you will see an additional overlay over your original targets. It should look similar to this below.
As you can see the circular radius targets the non targeted area produced from the first screenshot. It allows me to extend my reach to these areas, even though they maybe less populated or have little reach. Since they are still within the reach of the other cities the client is targeting, this overlay reach will help with the campaign. If the client wanted to only target selected cities then this strategy will play no part. Since they are targeting a county, this will work well.
This simple overlay radial targeting will help increase reach, even find leads which Google thinks their maybe none. In essence you want to get a good reach of users or visibility to your ad. You just do not know if these 'gapped' areas will not produce a lead to your client.
I would probably say to use this strategy only if there are missing areas within your map. I would not use this strategy if there are missing areas outside. It would defeat the purpose and the client may not travel out that far from their office or target area. If you are missing cities that are already surrounded by cities targeted already then it would make sense to include them by using a radial target.