Following the discussion from the last lesson, the barriers naturally found within the canvases themselves (e.g., Breakpoint's backbone and gorge, Boneyard's ship, and Spire's rise and crest) bring the concept of a barrier alive to the players. Players intuitively feel the presence of Tier 2 as they run around Tier 1, seeing just enough of it so that they are kept unconsciously aware there is more to the map. The barriers actually build cohesion between Tier 1 and Tier 2. Their mere presence prepares the players for what is to come next. They in effect foreshadow the other half of the map.
Other ways to create and strengthen cohesion with the Story is to ensure weapons and vehicles spawn only with their respective Species. It can break cohesion for any Halo campaign to have a Rocket Launcher spawn in the Elite strong hold, or a Banshee spawn in a Spartan garage. Maintaining cohesion between the weapons or vehicles and their respective Species maintains cohesion between the Game Play and the Story.
Neutral power weapons in areas of interest to control are ideal for BTB maps in which the two teams contest each other to control those areas and capture the power weapons. But this Game Play is counter intuitive to a campaign. Neutral weapons break cohesion with the Story, since their mere laying around would appear out of place and unbelievable in a real campaign.
Gating away forged objects for anything other than Bomb explosions or doors opening breaks cohesion - pure and simple. The proper way to handle video rendering performance degradation (Frame Rate) is to reduce block count and block density.
Do not open a new front for any Tier, but continue the same flow of Game Play, the same strategy of offensive push, by maintaining a linear path through out the Round by the proper positioning of Spawn Zones. Otherwise, a player pushing from the South suddenly finding himself spawning from the West can feel like a new front is opening and he must abandon his current strategy entirely. The Round can essentially feel like it is starting over, and the cohesion between the Tiers is destroyed outright.
Be careful not to build your map where things occur that don't make sense, seem unbelievable, or cause abrupt changes to the player's experience and strategies while in Game.
Summary
Barriers are a critical feature, a foundational Element of the Map, that builds cohesion between the first and second Tier and helps the map feel like one map.
Spawning weapons and vehicles by their respective Species builds cohesion between the Game Play and the Story.
Gating forged objects for other than Game Play experience, or opening new fronts at the transition of a Tier, are examples of how to break cohesion of Game Play.