Line of Sight

Line of Sight is a game mechanic introduced in Bloons TD 6. As its name implies, lines of sight apply to most towers when interacting with their placement near obstacles, causing parts of their range to be obstructed and unable to be uitlized at all. The effect is represented within the range of a tower, highlighting obscured portions of the range with a red boarder and area in place of the dark gray that range is typically represented as.

There are also instances where the effected tower has restricted lines of sight without any portion of its range being actively obstructed. This occurs when considering towers that utilize infinite range aside their actual range, such as the Sniper Monkey's small range around itself versus its actual range that covers the whole of the map, which itself can be blocked by objects. A similar occurance is present with the Advanced Intel upgrade for the Monkey Sub, gaining the representation of blocked lines of vision with or without a tower present in that blindspot.

Objects
Objects are the group of structures and items present in BTD6 that serve to interfere with the Lines of Sight for towers placed in the game. They tend to be placed either on the outskirts of the map or near the center, as to minimize and maximize their presence as line of sight blockers. Another irritating aspect is that contact with any of these objects will cause projectiles to be used up, even if they had a high pierce that was still to be used on the bloons.

Most maps have at least some form of objects, with more prominent obstacles being a special sub-category of Removable Objects.

Permanent
Permanent Objects serve as the general sight line blocker for most maps, with the likes of Logs, Tree Stump or Hedge using them to limit the potential of towers as well as making the tracks more challenging to justify their longer track lengths. Hence, most of the permanent objects that majorly obstruct the track are found in Beginner difficulty, though there are examples outside this difficulty.

Removable
Removable Objects are found in Intermediate and Advanced difficulty maps, functioning near-identical to normal objects except for one aspect: they can be payed for so that the area they inhabit can be transformed, often in the favor of the player. Most of these objects serve to only block off portions of the map to place towers upon, as well as obscure the sight lines of towers. A lone exception to this rule is the removable object in #ouch, which changes out a water-filled hole in the center of the map with normal land, unrelated to sight lines, but purely conversion of terrain.

Exceptions
As there are many towers afflicted with blindspots when combating alongside objects, there are several examples of tower that completely or partially bypass these obstacles.

Towers and Upgrades
Of all the towers in the game, the Monkey Ace and Heli Pilot naturally bypass any and all obstacles in BTD6, having their projectiles not be deflected by objects as well as ignoring sight line blindspots due to how they function. The Alchemist and the Spike Factory on the other hand also ignore objects by default, as their projectiles and spikes are shown to the throuwn over these, literally hurdling over objects to hit their targets. Obyn Greenfoot has the interesting perk of being able to fire through objects by default.

While the splash damage from Bomb Shooters does get obstructed by objects, the Ice Monkey can still damage bloons obscured by an object. This is accomplished by having other bloons float into a non-blondspot, causing the rest of the bloons in the Ice Monkey's Radius to be caught in the ice blast, regardless if they were behind a blindspot or not.

The Aircraft Carrier and Carrier Flagship gain the ability to ignore obstacles with their subsequent planes, though their primary guns can still be plagued with blindspots.

The Wizard Monkey is able to bypass line of sight obstruction once Arcane Mastery is purchased.

The Sun Temple and the True Sun God allow the Super Monkey to fire over objects onto the bloons.

Highground
On specific maps, there are certain locations where a tower or multiple towers can bypass any and all forms of objects, allowing for a good vantage point for towers that are most hindered, like the Sniper Monkey. Instances include the large stump in the center of Tree Stump, or the vacant crow's nest in Off the Coast.

Alternatively, Highground can be simulated by use of the Carrier Flagship, allowing towers placed upon it to bypass objects themselves.

Trivia

 * There is a Line of Sight option in the pause menu, which hides both the Range and Lines of Sight of a selected tower.