“The cars are on the wrong side,” Arhu said suddenly.

“Not wrong,” Rhiow said, “just different. There are places on the planet where they don’t drive the way ehhif here do.”

“No one on the planet drives the way ehhif here do,” Urruah muttered.

Rhiow put her whiskers forward in a smile. “No argument.”

People were walking back and forth before what would be the aperture of the gate, were it physically to open. “Look at them all,” Arhu said, somewhat bemused. “It keeps coming up cities.”

“It would whether Urruah had set the parameters that way or not,” Rhiow said to Arhu. “Worldgates inhere to population centers.”

Make it a little dryer for him, why don’t you? Urruah said good-humoredly into her mind as he looked out at the ehhif hurrying by. “See, Arhu, if you pack enough people of whatever species into a tight enough space, the fabric of physicality starts fraying from the pressure of all their minds intent on getting what they want. Pack even more of them in, up to the threshold number, and odd things start to happen routinely in that area as the spacetime continuum rubs thinner—places get a reputation for anything being available there, or at least possible. Go over the threshold number, and gates start forming spontaneously.”

“Much smaller populations can produce gates if they’re there for long enough,” Rhiow said. “The piled-up-population effect can be cumulative over time: there are settlements of ehhif that have been established for many thousands of years, and therefore have gates even though only a small population lives there at any one time.”

“Catal Huyuk,” Urruah said, “and Chur, places like that. Those old gates can be tricky, though: idiosyncratic … and over thousands of years, they pick up a lot of strange memories, not all of them good. The newer high-population-locus gates can be a lot safer to work with.”