Portal networks could be ad hoc or have some sort of organization with their call signs. An idea with some thoughts. Slight wall of text so be warned:
There would be three type of dial numbers:
- Public - This is for the network of public portals people use for general exploration and fast travel.
- Property Entrance - This network is the front gate for all permanent server residents plots. Once they choose a plot, they would get the supplies from the server or have marked out where their entrance portal would be. Numbers would likely be optional listed/unlisted.
- Local - These networks are claimed and used by players or occasionally the server for specific local purposes. This includes in base/land transport, dungeons, etc. They should not be listed in public lists to avoid clutter.
At the beginning of every portal address would be 2 call signs known as the Network ID. The Public and Property Entrance networks each have a single ID. Local networks have one ID unique to each network. This should keep people from spilling over.
On Property Entrance numbers there would be an additional 3 symbols. This should leave plenty of unique Property numbers so everyone have one.
Local numbers would have an additional 4 symbols to utilize. This should leave plenty of available portals for at least a couple local projects per Network ID.
Public numbers would be the most complicated. First you would have a 3-5 call sign Hub ID. This routing ID tells you the abstracted route you took from the center portal to the portal hub where you land. Second is a 3 call sign Portal ID. The main hub with nice structure around it would have a default 000 type Portal ID. This is useful if their are fun or useful features near a particular hub. It would also add some coherence to any server maps that are eventually made.
I see two possibilities for how public portals are arranged.
First is the Cartesian grid. The Hub ID would be the next step you take (N/S/E/W/SW/SE/NW/NE/0). It is easy to calculate where new hubs should be located and write numbers. Unfortunately there would be a lot of possibilities for each number, although a lack of numbers should not be an issue.
Second is the Polar grid. The Hub ID would be a radius and which quadrant relative to the center the Hub is in. This would require a little trigonometry to figure out new hub locations. Also reading the hub address would not give you as much a sense of journey as the Cartesian grid. However it would use less numbers making creating numbers easier.