Set your range in the scanner to zero.
This will receive only the sites/agency's you are in range of the programmed ranges.
So many of the programmed site/agency ranges are well in excess of the areas they actually cover.
I highly recommend you use scanner software to refine the various individual ranges to meet your needs.
I had to do this living in So. Calif. otherwise I would hear agency's dozens of miles from where I'm actually at.
If your scanning the full db, do as suggested above. If your scanning a favorites list, do as suggested as above, and also go into the favorite list (containing the system) options and set Location Control to ON
A little more explanation: Range is a difficult concept to grasp for the new listener. It is NOT where you press the RANG button and the scanner "listens" to just those things that are within the selected Range.
Rather, there are two different Range concepts (for a trunked system), Site Range and Department Range. For the Site Range, it is an assumed value of how far a transmitter will transmits and where it is located.
For Departments, this is set per Radio Reference Standards, the location is the approximate geographic center of a geo-political jurisdiction (as in city, county or state, etc.) The Range is about how large the jurisdiction is. (Great if such things were circles or rectangles.)
It is possible, actually quite likely, you could hear a Department well past a jurisdiction's boundaries. In fact there is a city about 40 miles south of me that is limited to a Range of 10 miles, because that's how big the city is. However if I set the Range to 50 miles, I can still hear this city.
In conventional systems, those Ranges are the size of the city and also the Location of the transmitter.
So think of three circles. One is where your scanner is. The second is where the Site is and how far it reaches out. The third is where the Department is and how big its jurisdiction is. If all three circles overlap, your scanner will attempt to "listen."
You can "enlarge" the circle of your scanner by increasing the RANG value. There are pros and cons to have large/small scanner/global Range values. You just gotta tinker and find what suits your fancy.
Lastly you can create a Favorites List, import stuff from the master database. You can adjust the Site and Department Ranges as you want, just like I did for that 40 mile away city.