Technology tree

In strategy games, a technology, tech, or research tree is a hierarchical visual representation of the possible sequences of upgrades a player can unlock (most typically representing the research progress of a given faction). Because these trees are technically directed and acyclic, they can more accurately be described as a directed acyclic graph of technologies. The diagram is tree-shaped in the sense that it branches between each 'level', allowing the player to choose one sequence or another. Each level is called a tier and is often used to describe the technological strength of a player. Typically, at the beginning of a session of a strategy game, a player will start at tier 1, which offers only a few options for research. Each technology that a player researches will normally open up one or more new options, but may also, depending on the computer game, close off the paths to other options. The tech tree is the representation of all possible paths of research a player can take, up to the culmination of said sequence. A player who is engaged in research activities is said to be "teching up", "going up the tech tree", or "moving up the tech tree". Analysis of a tech tree can lead players to memorize and use specific build orders.