Portal

A portal is an invisible marker in The Sims 2 that the game uses to mark where Sims, NPCs and vehicles spawn and de-spawn on a given lot. Every lot in the game has its own preset portals that are invisible and unselectable by default. There is no in-game method to edit them, but they can be made visible and selectable through the use of the Portal Revealer Mod.

Pedestrian
Pedestrian portals determine the place where any walk-by Sims enter and exit the lot. These portals are also used by stray pets, some NPCs, and Sims in the active household if they leave or enter the lot on foot. Every lot contains two of these markers, located on the second grid square from the edges of the sidewalk. When a Sim, stray, or NPC is spawned, the game will randomly choose one of the two portals and will spawn them there. When a Sim, stray or NPC starts to leave a lot, the game will route them to the nearest pedestrian portal to their location.

Car start
The car start portal marks the place where Carpool cars and Taxis spawn. Any Cars owned by the active household will also appear from this spot. Every lot has at least one car start portal. If the portal spot is covered, the car will spawn in the next empty place in a straight line forward from the marker. If there's no place for car to appear, the car will be frozen outside of the lot until there's enough space for it to appear.

Car stop
Vehicles spawned from the car start portal drive to the car stop portal where they will stop, allowing the Sims inside to exit. If something is blocking the car stop portal, the car will stop earlier. Every lot has one car stop portal, usually near the mailbox.

Car service start
The car service start portal marks where most NPC service vehicles (such as the maid's van or the repairman's truck) spawn. The portal is located in the opposite lane as the car start portal.

Car service stop
Vehicles spawned at the car service start portal drive forward to the car service stop portal. Any carpool helicopters will also land in this spot.

Beach
These portals are automatically generated on the shore of beach lots.

Effect holder - beach waves
These portals are located on the far ends of the Beach lot under the water. The portals are used to generate wave effects.

Mailbox or telephone booth
The mailbox (on residential lots) or telephone booth (on community lots) also serves as a portal. They determine the location to which walk-bys go after spawning from one of the pedestrian portals, and where the move-in cut-scene is played. They also mark the spawn location of some NPCs, such as Witches.