There are hundreds of thousands of cell towers in the United States - over 400,000 as of 2020. These sites receive and transmit the radio frequency signals emitted by your cell phone, allowing you to send and receive communications and data ranging from phone calls to YouTube videos. They make up the network that enables us all to connect with one another as well as access the internet and other cellular applications. The connectivity between various cell towers and our cellular devices makes cell triangulation possible.
Cell Phone Towers are generally built and maintained by tower companies or wireless carriers. Carriers may lease towers they don't own from either private parties or other carriers. Towers can be situated on mountaintops or buildings, be disguised as trees, or otherwise blended into a rural or cityscape. Their proximity and the availability of their bandwidth combine to determine which tower you will be connected to, and how powerful your signal/reception will be.
Proximity and Number of Users
If you've ever been to a large gathering of people, you may have experienced issues using your cell phone despite your screen showing connectivity. This is due to the increased number of people taxing the cell towers in range. While the United States has a large number of cell sites, denser in more populated areas, they are not necessarily designed to accommodate an unusual glut of users. While this is an extreme example, in general, the number of users connected to a cell tower does significantly impact which tower you will be connected to. You may be located within a few feet of a cell tower but actually connected to a different one out of view several miles away. Knowing which towers you have connected to as your phone transmits and receives data is the basis for Cell Triangulation - or determining location based on cell phone data.
An Imperfect Science
Triangulation is not an exact science. You may not be connected to the tower closest to you, and depending on the carrier, you may actually be connected to more than one tower simultaneously. However, you can determine the cell tower's coverage area and draw a circle around it - the phone must have been within that circle to connect. As a cell phone travels, it will connect to a different tower - and another circle can be drawn. If the phone was connected to multiple towers at once, you could see where these circles overlap to hone in further.
Using the latitude and longitude of the connected cell tower as your reference point, the location could be further narrowed by utilizing the antenna sector, a direction referenced in 0 - 360 degrees that indicates the side of a cell antenna used for processing that connection. Additionally, the antenna beam width can be used for further precision in directional location. The denser the number of towers (such as in a large city), the more accurate this approach can be. In rural areas, a cell tower may cover a large swath of land, reducing the specificity of the coverage area.
While this technique is not as accurate as analyzing a GPS device which would have specific latitude and longitude coordinates, it can still be of enormous power to prove or disprove a statement or an alibi in a court case. Being able to say someone was where they said they were can have considerable implications in cases ranging from a custody battle to a murder.
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