In the center of City Z, there are numerous large buildings, so there is a possibility that a portal could suddenly appear somewhere in them.
So a portal breach disaster like the one that happened in Security Area Z4 just a few weeks ago becomes not only much more likely, but also much more dangerous, considering the millions of people who live in City Z. For this reason, portal detection tools and technologies were spread throughout the city, so that portals began to be detected seconds after they appeared due to their radiation.
