Item 2. Properties

Offices

Our principal corporate headquarters is owned and located in Houston, Texas. In addition, we have offices throughout the U.S. in locations convenient for the management and operation of our communications infrastructure, with significant consideration being given to the amount of our communications infrastructure located in a particular area. We believe that our facilities are suitable and adequate to meet our anticipated needs.

Communications Infrastructure

We own, lease or manage approximately 40,000 towers geographically dispersed throughout the U.S. Towers are vertical metal structures generally ranging in height from 50 to 300 feet. Our customers' wireless equipment may be placed on towers, building rooftops and other structures. Our towers are located on tracts of land that support the towers, equipment shelters, and where applicable, guy-wires to stabilize the tower.

Additionally, we own or lease approximately 60,000 route miles of fiber primarily supporting our small cells and fiber solutions. The majority of our fiber assets are located in major metropolitan areas. Our small cells and fiber are typically located outdoors and are often attached to public right-of-way infrastructure, including utility poles or street lights.

See "Item 1. Business—Overview" for (1) information regarding our tower portfolio including our land interests and for a discussion of the location of our towers, including the percentage of our towers in the top 50 and 100 BTAs and tenants per tower and (2) information regarding our fiber portfolio including a discussion of the location of our fiber. See "Item 7. MD&A—Liquidity and Capital Resources—Contractual Cash Obligations" for a tabular presentation of the remaining contractual obligations related to our business as of December 31, 2017.

Approximately 53% of our towers are leased or subleased or operated and managed under master leases, subleases, or other agreements with AT&T, Sprint, and T-Mobile. We have the option to purchase these towers at the end of their respective lease terms. We have no obligation to exercise such purchase options. See note 1 to our consolidated financial statements and "Item 1A. Risk Factors" for a further discussion.

Substantially all of our communications infrastructure can accommodate additional tenancy, either as currently constructed or with appropriate modifications. Additionally, if so inclined as a result of a request for a tenant addition, we could generally replace an existing tower with another tower, replace a small cell network antenna with another antenna or overlay additional fiber in order to provide additional coverage or capacity, subject to certain restrictions.