Visualization of different tower footprints in Bloons TD 6
Footprint is the area of space that a tower occupies when placed in a map in the Bloons TD series. A tower can only be placed if its footprint does not overlap any other towers' footprints or terrain the tower cannot be placed on. A footprint is usually either a circle (defined by a radius) or a rectangle (represented by height and width). Easier maps tend to have more open spaces for placing larger or higher amounts of towers, while harder maps often limit the amount of space that towers can be placed on (sometimes preventing certain towers from being usable at all).
When placing a new tower, the player must make sure to have enough open space to place it beforehand, as a new tower cannot override area that is already occupied. Players can remove the towers that use the desired space, usually by selling them.
This section is incomplete. You can help out by expanding it. The editor who added this notice elaborates: differences between flash version, dsi, mobile ports
This section is empty. You can help out by adding to it. The editor who added this notice elaborates: differences between DSI, Mobile ports and flash version
Bloons TD 5
This section is empty. You can help out by adding to it. The editor who added this notice elaborates: differences between flash/deluxe and mobile/console. Also does BMC and Battles deserve its own sections?
Bloons TD 6
Showcase of tower footprints in Bloons TD 6, where the area that the tower actually uses is indicated in green to show correspondence with the in-game model.
In Bloons TD 6, the majority of towers, powers and other items that can be placed on the map have a circular footprint, with a few exceptions, listed on the table below. Despite all towers having an internal "footprint radius" defined (or height and width for rectangular forms), they have separate flags that determine their behavior, as they can block other tower placements, which this is true for the vast majority of towers, however some sub-towers do not have this flag active like Engineer Sentries or Mini-Sun Avatars. This is also true for powers like Pontoons and Portable Lakes and the footprint is used instead to determine the amount of available space for other towers that are placed over them.
Powers and items can also have flags to ignore collisions with towers and/or the capability of be placed at any point of the map, even over obstacles or the Bloons path, examples include the Mega Mine from Admiral Brickell, the totem of The Final Harmonic or Geraldo'sKiller Rabbit.
The air unit of towers that are linked to a base (Heli Pilots, Monkey Aces and Rosalia) technically do not have a footprint but in Rosalia's case it does create a placement block of 6 units around her which acts as a footprint and is removed when she reaches level 7. However, the planes from a Sun Temple of True Sun God are treated as sub-towers and not as air units, and they have a footprint with a radius of 1 unit, which is located in the same place as their parent tower (it can be seen in the image above by zooming into the VTSG).
Some maps can have areas where players can place towers where they visually wouldn't fit (e.g. the altar in Encrypted) and in the other hand, there are also places where towers that can fit are restricted, for example, Heli Pilots cannot be placed in on the top right section of Erosion, but Banana Farms can despite having a larger footprint.
Towers and Heroes do not change their footprint when they are upgraded, even if the model is visually larger, which is specially evident on Paragons, however, this behavior has one exception, which is when a Sun Avatar is upgraded into a Sun Temple, in this case the footprint grows from a radius of 8 units to a rectangle with a width of 37 units and a height of 40 units. This usually does not have any interactions with other regular towers as they are sacrificed when the upgrade is purchased, however as the Sun Temple cannot sacrifice Powers or Heroes, if they are placed right next to the Super Monkey before being upgraded, they will end up inside of the Sun Temple's footprint, this interaction does not impact the towers and can bet moved away by using the Redeployment ability of a Support Chinook,
This behavior is usable in Freeplay strategies to save space for Tech Bots by placing them around Super Monkeys that are intended to become Sun Temples later in the game. Also, there is a small window of time after purchasing the Sun Temple where after the Monkeys around it are sacrificed but before its footprint grows, which can be exploited by using a Support Chinook to move a tower right next to the Sun Avatar during the transform animation so it ends inside the Temple's footprint.
Optimal placements of towers with the same or different sizes within a certain area is a common problem that is found in recreational mathematics, known as circle packing, and despite the intuition of going for hexagonal or triangular patterns (where the form indicates the arrangement of the center of the circles) are usually not the optimal solution. Although procedures exist for regular forms, the variety of shapes of open areas in maps in BTD6 makes finding optimal solution it a difficult task that usually can only be solved by a brute force trial and error approach.
