After unlocking ctOS Centers you’ll only have a part of the district uncovered. Similar to viewpoints in Assassin’s Creed, ctOS Towers place markers on important locations and point out collectibles and side missions.
SMG-11 Weapons (Complete 1 ctOS Tower)
Amargosa Turbo Vehicle (Complete 5 ctOS Towers)
Clear Signals Trophy/Achievement (Complete all ctOS Towers)