Item 2. PROPERTIES

As of December 31, 2019, we owned and operated a portfolio of 179,520 communications sites, including 1,774 DAS networks. 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 consist 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, in some cases, one or more equipment shelters that house a variety of transmitting, receiving and switching equipment. In addition, many of our international sites typically include power generators and batteries, which are often used for primary power in lieu of an electric grid connection in select markets. The principal types of our towers are guyed, self-supporting lattice and monopole, and rooftop towers in our international markets.

U.S. Property Segment Encumbered Sites. As of December 31, 2019, the loan underlying the securitization transactions completed in March 2013 and March 2018 (the “2013 Securitization” and the “2018 Securitization”, respectively, and together, the “Trust Securitizations”) is secured by mortgages, deeds of trust and deeds to secure the loan on substantially all of the 5,114 broadcast and wireless communications towers and related assets owned by the borrowers (the “Trust Sites”) 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 3,542 communications sites owned by subsidiaries of the issuer (the “2015 Secured Sites”).

Asia Property Segment Encumbered Sites. There are no encumbered sites in our Asia property segment.

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

Europe Property Segment Encumbered Sites. There are no encumbered sites in our Europe property segment.

Latin America Property Segment Encumbered Sites. Our outstanding indebtedness in Brazil is secured by an aggregate of 760 towers and outstanding indebtedness in Colombia is secured by an aggregate of 3,563 towers.

Ground Leases. Of the 177,746 towers in our portfolio as of December 31, 2019, approximately 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, 43% of the ground leases for our sites have a final expiration date of 2029 and beyond.

Tenants. Our tenants are primarily wireless service providers, broadcasters and other companies in a variety of industries. For the year ended December 31, 2019, our top four tenants by total revenue were AT&T (22%), Verizon Wireless (15%), T-Mobile (10%) and Sprint (8%). Across most of our markets, our tenant leases generally have initial non-cancellable terms of five to ten years with multiple renewal terms. As a result, approximately 65% of our current tenant leases have a renewal date of 2025 or beyond.

Offices. Our principal corporate headquarters is leased and located in Boston, Massachusetts, where we currently lease approximately 40,000 square feet of office space. We also own or have entered into long-term leases for the majority of our facilities in international and regional locations for the management and operation of our property and services businesses, including offices in each of our U.S., Asia, Africa, Europe and Latin America segments. We believe that our owned and leased facilities are suitable and adequate to meet our anticipated needs.