A "link" usualy has 2 files/sprites. It's neither like 3D objects nor like hard objects. The avatar can not go behind it. He can only to collide with the "shadow" (figure having the sufix "S") that will transport him to another place that can be another Lot, another City or a "normal" web-page. The Z of a "shadow" is: 0. The Z of a link is 12, like any of the hard objects.
Take a look of some "links" working at this LOT.
The basic "link" is that to go to a "normal" web-page:
At the "normal" web page you need to put a link to go back to the Lot of OLPCity you came from. The icon to be clicked you see at right.
A link to go to the next Lot,we call it Transit. Not two files here. It's a green paralelogram:
To go from a Lot to inside a "house" of the lot we have only a "shadow for collision":
Read the lesson Inside a house to understand this better.
The "gates" are links to a distant Lot or to another OLPCity. If he likes to go to any other Lot, he collides with the "gateS" (a "shadow for collision").
An special "link" is the "Time-Space Portal" used to go to (and return from) another "time" (by example the year 2000 A.C.) or "space" (another planet) . It's like one of the Animated objects but has a "shadow" to be collided by the avatar and another to make the transportation to other place.
The heroe of OLPCity (the kid, the avatar, you ) works for the Times-Space Inc. and he needs to do some travels in the time and space. In the time he will do some researchs talking to people of different times about how they really live at 2000 A.C, 1800 D.C etc. In space, he will go to the planet "Pink" where there are the "gold beans" he needs to collect - they are very valuable. But he will have some chalenges to do it. It's the non-educational part of the project. Only funny games.
Take a look to a "Time-Space Portal" working at this LOT. Wait a little because there are many images to be downloaded (the browser of the OLPC station only opens the page after all the images are downloaded but the IE works differently).
You can see at this exercice, a Time-Space Portal that will make you go to the Pink planet : http://www.dmu.com/olpctut/tut5e.html.