GPS

The giant facility took up more space than 650 domed stadiums, but the construction equipment was attacking inside the building. The controlling radio signal had to be fairly strong in order to make its way through all the walls. For someone who could freely control electricity like Mikoto, it was like having the GPS function of a child’s cell phone on.

She knew what path she had to take, so all that was left was to follow it.

Toaru Kagaku no Railgun SS2, Chapter 3, Part 8