It’s hard to say. I know one of the nodes I’ve deployed can directly see another node about 30km away but that is with a 5dBi antenna and is positioned on the side of a hill overlooking the city so had good line of sight. With a 2dBi antenna on a portable node I’ve been able to get approx 10km with reasonable line of sight. 

 oh nice - it not fixed - weather - dB gain - directional only antenna incrase range a lot + LoS
2dBi 10Km 400Mhz band 900Mhz little less - about few KiloBytes/sec BW not bad at all 

 big cities PROBLEM / noise / jamming / building- rural n nonpoluated areas with no cell phone tower best 

 We are pretty lucky here as the city is surrounded by hills so we have a lot of nodes on top of the hills which gives pretty good coverage across the city. Plus a good community that works together fairly well to avoid nodes interfering with each other.