Portals

Portals is a technical name for invisible markers in The Sims 2 that the game uses to determine special locations.

Obtaining
Every lot in the game has it's own preset portals that are invisible and unselectable by default and there's no in-game method to edit them.

The only option to make them visible and editable is using the Portal Revealer Mod

Pedestrian
This portal determines the place where any walkby sims enters and exits the lot, including some NPCs and controlled familly if they leave/enter the lot on foot. Every lot contains two of these marker located on the second grids from the edges of the sidewalk, the game randomly selects one of the portals when spawning a sim, but when leaving, sim will always chose the nearest.

Car Start
Marks the place in which Carpool cars and Taxis will spawn. Player's familly Cars will also appear from this spot. Every lot has at least one portal. if the 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 untill there's enough space for it to appear.

Car Stop
Vehicles spawned from the Car Start portal will drive to the Car Stop portal where they will stop, allowing the sims inside to exit, if something is blocking the place, the car will stop earlier. Every lot has one Car Stop portal, usually near the Mailbox.

Car Service Start
Same as Car Start portal, but is located on the second lane and is reserved for Service vehicles.

Car Service Stop
Same as Car Start portal, but is located on the second lane and is reserved for Service vehicles. Player's Helicopters will also land in this spot.

Beach
These portals are automatically generated on the shore of the Beach lot.

Effect Holder - Beach Waves
These portals are located on the far ends of the Beach lot under the water, they only purpose is to generate a wave effects.

Mailbox and Telephone booth
Mailboxes and Telephone booths also serve as a portals, they determine the location to which walkbys have to go to after appearing from the Pedestrian portal and where the move in cutscene is supposed to be played, they also mark the spawn location of some NPCs such as Witches.