No such thing - it is what it is - the numbers are a very broad generalisation. My distance record is +118km using iffy antennas. There are a load of posts on here with people getting a few hundred meters.
Not really, probably only a very misguided attempt by academics who haven’t got out much.
Reality is everything - we do an RF survey for terrain, look at the bigger sticky up structures, come up with an educated guess, deploy some gateways, map it all, move some of them, map again, put in some in-fill gateways where there are bigger blank spots, rinse, repeat, watch a new building mess it all up, have new client put a tonne of devices where coverage is ropey, have a really useful gateway lose it’s home, see a new device deployment tip a gateway in to a level of overwhelm, have a new mobile tower introduce just enough interference to mess up a patch of coverage, new municipal refuse vehicles that start parking close to antennas, blocking signals for an hour at a time, etc etc etc.
All of this tends to happen in slow motion so it’s not a fire-fight.
Your very best bet is to learn about RF - antenna polars, Fresnel zone, signal strength vs distance (square root sort of stuff) - that’s a few hours well spent so you understand what is going on.
Then get a packet of Smarties, eat them, remove both end caps, cover the tube in Duck Tape, et voila, you now have a Line of Sight survey tube. If you stand where the gateway antenna is and look through the tube, if you can see a device location, you’ve a fighting chance of getting a signal through as long as there is nothing big and sticky up in that line, if there is anything big and sticky dangling down, it’s probably an alien mothership.
Then pick an area, deploy a gateway, map. Then move the gateway to somewhere topographically different, map. Do that again.
This should give you far more knowledge & understanding than any random “how to cover a city” type text. And with the aid of Google Earth / StreetView you can look at what the shapes are & which buildings may get in the way to extrapolate your learning.
Bear in mind that some buildings are relatively RF see-through and some buildings are unexpectedly RF blockers - it’s all in the construction - steel frame, concrete, metallic cladding etc.
You could look at TTN Mapper but you need to find an urban area that has a modest number of gateways - so Amsterdam (the home of TTN) doesn’t count. You want an area that has been reasonably well mapped and, using Google, look at the coverage vs terrain/buildings.