We are a leading independent owner and operator of wireless communications infrastructure, including tower structures, rooftops, and other structures that support antennas used for wireless communications, which we collectively refer to as “towers” and the location of the towers as “sites.” Our principal operations are in the United States and its territories. In addition, we own and operate towers in South America, Central America, and Canada. Our primary business line is our site leasing business, which contributed 98.0% of our total segment operating profit for the year ended December 31, 2018. In our site leasing business, we (1) lease antenna space to wireless service providers on towers that we own or operate and (2) manage rooftop and tower sites for property owners under various contractual arrangements. As of December 31, 2018, we owned 29,578 towers, a substantial portion of which have been built by us or built by other tower owners or operators who, like us, have built such towers to lease space to multiple wireless service providers. We also managed or leased approximately 9,700 actual or potential sites, approximately 500 of which were revenue producing as of December 31, 2018. Our other business line is our site development business, through which we assist wireless service providers in developing and maintaining their own wireless service networks.
Our primary strategy is to continue to focus on expanding our site leasing business through organic growth and expansion of our tower portfolio to create shareholder value. We believe that the long-term and repetitive nature of the revenue stream of our site leasing business will permit us to maintain a stable, recurring cash flow stream and reduce our exposure to cyclical changes in customer spending which arises in our site development business. Key elements of our strategy include:
· Maximizing our Tower Capacity. We generally have constructed or acquired towers that accommodate multiple tenants and a majority of our towers are high capacity tower structures. Most of our towers have significant capacity available for additional antennas, and we believe that increased use of our towers can generate additional lease revenue and be achieved at a low incremental cost. We measure the available capacity of our existing sites to support additional tenants by assessing several factors, including tower height, tower type, wind loading, environmental conditions, existing equipment on the tower and zoning and permitting regulations in effect in the jurisdiction where the tower is located. We actively market space on our towers through our internal sales force. As of December 31, 2018, we had an average of 1.8 tenants per tower structure.