Transmat Portals

Though the theoretical possibility of transmat technology was revealed by the work of the renowned physicist Fr. Borland Barnes in the early years of the twenty-third century it was not until the middle of that century that transmat portals became a reality.
Large masses in real space are reflected in subspace topology as gravitational plateaus separated from the subspace ground plane by massive gravitational shear planes. The plateaus float on the subspace ground plane their isolation from the rest of subspace imposed by the destructive shear planes.
A transmat portal is a subspace gate, which is made by using a hyperspace drill to create an opening to subspace which is located on the gravitational plateau which is the reflection of a world. It is connected to another portal which opens out to normal space at another location on the same plateau, the same world. The hyperspace drill creates the virtual tunnel which allows the gates to be placed back to back in subspace yet open to portals many thousands of miles apart in real space.
In the early years of their construction transmat gates were rare and most often used to supplement other forms of transportation. A high speed train or road which goes through a transmat portal can span continents in an instant. As transmat technology became cheaper to utilize public pedestrian transmat portals become common. Eventually private transmat portals were possible to allow those who could afford them the capability to go from an office or apartment in the city to a home on a tropical island in an instant.
An individual transmat portal opens exclusively to its matching portal. Each gate is placed utilizing a hyperspace drill. No action by the user of the portal is required. They just have to step through.  It is possible to have many transmat portals in the same area, all leading to different destinations. However a large number of subspace openings in an area does require that the subspace structure be gravitationally fortified. This is one of the functions of the hyperdrill, to stabilize subspace topology in an area where a large number of gate portals have been constructed.
On TL B worlds it is still common to see individual gates which lead to a single destination. On TL A worlds it is much more common for public transmat portals to be located at transmat terminals. A transmat terminal has a large number of gates, usually arrange in some kind of logical sequence, leading to various remote locations. Some of them will lead to other terminals. Others to single remote gate portals. There is often a nominal fee for using a portal, typically no more than a milli or two, although some portals are free to use. For example, the Blakely Square portal leading to the Shrine of Our Lady of WoodSocket  does not charge a fee for use. There is usually not a separate fee charged to passengers if a train uses a transmat portal on its regular route. There may be a toll if a road utilizes a transmat portal.