I am scanning a planet for hidden cities. Do I have to be on top of a hidden city to see it, or is it enough if the city is in the range of my sensors?
The first possibility would mean that I have to visit each location of the planetary grid and -- to be honest -- that would suck.
There isn't a specific 'Scan for Hidden Cities' button yet. The only way you'd find them is by trying to land on a grid or by trying to build a city there.