12. Business Segments The Company operates in two business segments: rental and management and network development services. The rental and management segment provides for the leasing and subleasing of antenna space on multi-tenant towers and other properties for a diverse range of customers primarily in the wireless communications and broadcast industries. The network development services segment provides third party services that are complementary to the Company s rental and management operations and that facilitate the addition of new tenants and equipment on the Company s towers, including site acquisition, zoning, permitting, construction management and structural analysis. The accounting policies applied in compiling segment information below are similar to those described in the Company s Annual Report on Form 10-K for the year ended December 31, 2008. In evaluating financial performance, management focuses on segment gross margin and segment operating profit. The Company defines segment gross margin as segment revenue less segment operating expenses excluding depreciation, amortization and accretion; selling, general, administrative and development expense; and other operating expenses. The Company defines segment operating profit as segment gross margin less selling, general, administrative and development expense attributable to the segment, excluding stock-based compensation expense and corporate expenses. For reporting purposes, the rental and management segment operating profit and segment gross margin also include interest income, TV Azteca, net. These measures of segment gross margin and segment operating profit are also before interest income, interest expense, loss on retirement of long-term obligations, other (expense) income, noncontrolling interest in net earnings of subsidiaries, income on equity method investments, income taxes and discontinued operations. The Company s reportable segments are strategic business units that offer different services. They are managed separately because each se