How do police-scanner radio apps work? Specifically, where are they obtaining the streaming audio data?

Consider this popular mobile app that lets you tune into local police radio chatter.

How exactly do these applications work? They aren't using any built-in radio receiver in the phone, since you can also choose to listen to the radio stations of far away cities.

Is the operator of this application literally going out and setting up transmission arrays in each city before piping the collected data into the cloud? This seems rather expensive and highly unlikely in such a small operation. Alternatively, are these apps just using some API service that I am not aware of?

Where are they obtaining all this streaming audio data? Does anyone have any idea?

Without internet they must be using a radio receiver chip in the phone.

With internet. Just google for some live radio broadcast sites. For example this site on first search result.

Then simply stream the audio.