The Net is basically a vast "potential space" constructed by linking together phone lines and fiberoptic control cables. The Ihara-Grubb Transformation algorithms that govern Net reality generate this space as a "wire-skeleton" topography of grids and shapes. Areas of high line resistance (old lines, garbled transmissions), appear as "mountains", while areas of low line resistance appear as plains and valleys, individual computer systems appear as ICONS or constructs created from millions of tiny "bits" of color and light, which, like video images or halftone photographs, can only be distinguished as individual parts by close examination. To simplify navigation through Netspace, the actual communications lines of the Net are represented as an endless blue-white grid. When an individual line must be located, programs within the Netrunner's cyberdeck locate the required lines or access points, and identify them with a bright red beacon light.
The Ihara-Grubb Transformations are also designed to take the relative position of a system into account in relation to it's contiguous Netspace. For example, a computer system high in a skyscraper will appear as an icon far up in Netspace. A system buried underground will be positioned roughly as in relation to the plane of Netspace as it is relative to the ground level in external reality (or Realspace). Both systems can be found in a Netspace location analogous to their real locations in their individual subgrids. A moving system will travel through the subgrids that are parallel to its travel in Realspace.
Any place a computer can be turned on and hooked into the NET is an extension of the NET into this universe. The Net is, as far as anyone can tell, potentially infinite - if you can link a computer to this communications web, you will automatically create a new section of the Net around that computer. Thus, new areas are created all the time, as more computers are hooked up and logged onto The Net.
Theoretically, you could put a radio/Net link into a long range spaceprobe and extend the Net into deep space. But it would take a looooong time to get to that area of Netspace, and it would take forever to do things, Ihara and Grubb theorized that an alien intelligence with a lot of power and a knowledge of Earth computer-tech could link to the Net over interstellar distances. Probably, it could not actually do anything; the best solution would be to beam a link to an orbital satellite, downloading a copy of the alien Al into the Net at this end, then move freely about the Net.
Some Netrunners claim this has happened already.