Gates, Gate keys, and Gate locks

[Agemegos]

Sorry about the wall of text. I have edited for brevity and focus.
the cost of creating a Gate using the rules for hiring wizards to cast spells is not expensive compared with a bridge, a road, or even a ship.

Amortising the cost of the gate over its expected number of transits before failure works out expensive. The cost of hiring a wizard with Create Gate or Control Gate, with apprentices or a ST battery to stand by ready to repair the Gate when it started to malfunction is expensive for a low-traffic route; quite affordable for a high-traffic route or if a number of Gates serving different low-traffic routes were co-located at a Gate nexus.

there are implications of infiltrators establishing Gates for the defences of cities and towns.

RE: trade through the Gate network. goods would flow from market to market through the network, finding the cheapest route even if no-one had the information needed or mathematical chops to solve that cheapest-route problem. the huge mixture of long-distance and short-distance links would mean that geographical distance is unimportant on Cidri.

"bottleneck" links in parts of the network, would produce huge wealth by charging tolls on them, or conducting a monopoly trade through them.Such middlemen could be cut out, by creating new Gates that circumvented theirs. So traders' guilds with very lucrative Gates would try to keep it secret where their Gates connected to, and might reserve them for trading through, and not allow toll-paying stranger to use them. Gates originally created for commercial use might have rules that do not allow any wizard to pass through them who has one end of a Gate set up — perhaps many Gates might not allow any wizard who knows Create Gate, Control Gate, or Long Distance Teleport to pass through them (except for their original creators and perhaps successors according to some rule).

Gate networks have strategic and logistical implications: discontiguous empires and so forth.

Gates are omniscient, which can be used for non-transport purposes: divination, security:. Imagine the research and intelligence-gathering applications of a Gate that will transport only pieces of paper with false statements written on them, or only witnesses who lie!