Item 2. PROPERTIES

Details of each of our principal offices as of December 31, 2017 are provided below:

In addition to the principal offices set forth above, we maintain offices in the geographic areas we serve through which we operate our tower leasing and services businesses. We believe that our owned and leased facilities are suitable and adequate to meet our anticipated needs.

As of December 31, 2017, we owned and operated a portfolio of 150,181 communications sites. See the table in Item 7 of this Annual Report, under the caption “Management’s Discussion and Analysis of Financial Condition and Results of Operations—Executive Overview” for more detailed information on the geographic locations of our communications sites. In

addition, we own property interests that we lease to communications service providers and third-party tower operators in the United States, which are included in our U.S. property segment.

Our interests in our communications sites are comprised of a variety of ownership interests, including leases created by long-term ground lease agreements, easements, licenses or rights-of-way granted by government entities.

A typical tower site consists of a compound enclosing the tower site, a tower structure and one or more equipment shelters that house a variety of transmitting, receiving and switching equipment. In addition, many of our international sites typically include backup or auxiliary power generators and batteries. The principal types of our towers are guyed, self-supporting lattice and monopole, and rooftops in our international markets.

U.S. Property Segment Encumbered Sites. As of December 31, 2017, the loan underlying the securitization transaction completed in March 2013 (the “2013 Securitization”) is secured by mortgages, deeds of trust and deeds to secure the loan on substantially all of the 5,178 towers owned by the borrowers (the “2013 Secured Towers”) and the secured revenue notes issued in a private transaction completed in May 2015 (the “2015 Securitization”) are secured by mortgages, deeds of trust and deeds to secure debt on substantially all of the 3,583 communications sites owned by subsidiaries of the issuer (the “2015 Secured Sites”).

Asia Property Segment Encumbered Sites. Certain of the outstanding indebtedness is secured by ATC TIPL’s short-term and long-term assets, including an aggregate of 41,306 towers.

EMEA Property Segment Encumbered Sites. Our outstanding indebtedness in South Africa is secured by an aggregate of 1,899 towers.

Latin America Property Segment Encumbered Sites. In Brazil, the debentures issued by BR Towers S.A. (“BR Towers”) are secured by an aggregate of 1,912 towers and the Brazil credit facility is secured by an aggregate of 145 towers. Our outstanding indebtedness in Colombia is secured by an aggregate of 3,563 towers.

Ground Leases. Of the 149,246 towers in our portfolio as of December 31, 2017, 90% were located on land we lease. Typically, we seek to enter long-term ground leases, which have initial terms of approximately five to ten years with one or more automatic or exercisable renewal periods. As a result, 50% of the ground agreements for our sites have a final expiration date of 2027 and beyond.

Tenants. Our tenants are primarily wireless service providers, broadcasters and other companies in a variety of industries. As of December 31, 2017, our top four tenants by total revenue were AT&T (19%), Verizon Wireless (16%), Sprint (9%) and T-Mobile (9%). Across most of our markets, our tenant leases have an initial non-cancellable term of at least ten years, with multiple renewal terms. As a result, approximately 50% of our current tenant leases have a renewal date of 2023 or beyond.