Starcraft 2 Zerg walling in strategies refer to the use of units or structures to create impassible barriers that prevent units from moving through certain obstacles. There are two main ways to wall units in, with structures or with units themselves. Walling in can be advantageous but can also be disastrous and redundant. How or why one chooses to wall in is of course based on their personal combat preference.
Also, walling in can be something that works against the Zerg player, rather than for the Zerg player. A Zerg player's strength lies in their ability to swarm opponents, utilizing the strength that comes with numbers. Individually however, Zerg units are generally rather weak compared to more specialized and more expensive units, like many Protoss units for example. It is therefore best to avoid being walled in by opponents if possible.
It is difficult for this civilization to wall in but it is possible. Also, placement of structures is subject, in the case of the Zerg, to the limitations of a player's Creep. Creep is the purple organic entity on which all their structures are placed. This can certainly cause problems.
For an ideal walling in strategy it would be best to use structures such as Evolution Chambers to create more narrow choke points. Make small exits about one or two unit sizes large through leaving openings, and build defensive structures close by. This is normally done against other Zerg opponents or Terrans looking to use speedy [censored] ions.
Another strategy which may be effective during team games would be one which uses the Nydus Network. Wall off your hatcheries so that no unit may enter your base, and create entry and escape points with Nydus Networks and Nydus Worms. A drawback of this, however, is that the Nydus Worms may be destro[censored] and your units will then be unable to go back to where they came from. When walling in, it is almost not always viable to use structures. Sometimes it is recommended you use units instead.
A good unit for a wall in tactic would be the Roach, for instance. These units have a tough carapace which gives them more hit-points than most ground units and they can therefore make for effective walls, especially on ramps.
Although it is difficult to use structures to wall in with the Zerg, Spine Crawlers can be placed side by side, and will prevent large units from slipping by them, however, smaller units can p[censored] by them like water through a strainer.
The terrain can work in a Zerg player's favor, however, and it may become advantageous to wall in with structures or it might not be. It may also be advantageous to wall in with units, these are purely situation based tactics. Knowing how to use your terrain is important and can mean the difference between victory or defeat, in some cases.
Therefore it's best to play your cards right, and not make costly mistakes. The advantage of units like Zerglings, for example, is that they can gang up on an a single enemy by surrounding them, so mobility in this sense is important, as ganging up on single units is the only way Zerglings are effective.
