Footprint

Footprint is the term given to the space taken up by a particular tower. The size of a tower's footprint is usually dependent on its power. Stronger towers usually have a larger footprint while the weaker towers usually have a smaller footprint.

Strategies

A very economic player that managed to put 11 Monkey Subs on a single Portable Lake

The size of the footprint can alter the strategies when trying to place strong towers on small pieces of land or water, where some towers cannot possibly rest on the part of the land or water.

In the Mobile and Steam games, turning on "Drop and Lock" in options will make it easier to place towers with different footprints. It will also help trying to align the tower as economically as possible for other towers to be placed, especially if there is tiny land/water space, such as on Pontoons or Portable Lakes.

In the Flash games, a common trick is to reduce the game quality to low. This slightly reduces tower footprints, allowing more towers to be placed.

On certain tracks, there is less space for towers to be placed, and thus making it harder towards the end game, due to most players typically adding Temples of the Monkey God with multiple sacrifices of large financial worth towards the end game. Tracks to be careful of include Space Truckin', Dockside, River Rapids, Cornfield, High Finance, and Peninsula.

Trivia

The Mortar Tower with footprint placement dependent on its barrel

• This is an official term as seen in the Bomb Shooter's Monkey Knowledge Card of Ranks 3, 8 and 13. It says "Footprint reduced by 5%/10%/15%" respectively.
• The Mortar Tower's footprint in BTD5 is the size of the barrel before the tower is placed. The tower can be moved at any position, and can be made to look as if it is on the track. Any more placements of any other Mortar Towers may be influenced by any other Mortar Tower barrels being already placed.