OK, before we even get started, I want to say that FlightGear is a pretty amazing progam, especially when as an end user it costs nothing. I've tried other Flight Sims and they all have problems one way or another, FlightGear does cover most aspects very well and better than many paid for products.
My one issue with FlightGear is ground scenery and in particular Urban areas. FlightGear takes information from openstreetmaps, which is fine, however does omit some of the finer details. What it does is take an area of housing and paints a generic overlay which fails to represent the actual area. Notably FlightGear also omits a lot of roads which can be seen from the screenshots that I have taken.
If you are flying large comercial style aircraft than you would be flying high enough to not see the problem, but if you are flying low altitude in a small aircraft, or helicopter, then the detail becomes more important, especially if you are flying by line of sight rather than using instruments for navigation.
Now, understandably there has to be a point where detail is best left out, the more detail required, the greater the processing power required to display the information. Many have expressed the desire to use satellite imagery however there is insufficient open source satellite imagery available that goes to the levels that google can go to, so in fairness openstreetmap is still the way to go for the foreseeable future. Also satellite imaginary also brings in unwanted artifacts on the ground so it is not a great way to go. It is apparent that many of the roads shown on openstreetmap are not used in FlightGear so I'm wondering how much extra processing power would be required to include some of those roads, and then overlay generic houses in those areas instead. I clearly do not expect each house to be drawn exactly as in real life but openstreetmap does show basic housing layout and I feel that this information might be extractable from openstreetmap and shown in at least 2D since the generic overlay is 2D anyway and I respectfully understand that some buildings such as tower blocks would still not be shown correctly. How much extra processing power would be required to do this. The end result certainly would be more recognisable for those areas.
I have written many programs in the past, I'm no where near the level you guys are, So I recognise just how difficult this will be to do, but if it was achievable then this would put FlightGear several steps ahead. I know you are not directly competing with the other software designers and that flight dynamics is far more important for a flight simulator, but I'm looking at this with the idea of extending the base technology that you are currently using and if achieved then maybe the same process could similarly used for the industrial areas, and so on.
For the purposes of the screen shots I'm using the latest stable release, FlightGear 2018.3.6, and using a Bluebird Explorer Hovercraft, since that can stop in any location at any height. I'm using ALS and maxed out every rendering option.
FG-1.png shows the area that I live, the estate roads do not exist in FlightGear but they are clearly shown on openstreetmap, what is also clearly shown on openstreetmap are the layout of the houses on that estate.
FG-2.png shows a Zoo that is fairly close to me, as seen openstreetmap clearly shows the Zoo and the roads around it, however FlightGear shows nothing in that area.
FG-3.png shows the Dartford crossing which is part of the M25, the crossing consists of 2 parts, the tunnels and the Queen Elizabeth Bridge which has been there almost 30 years, again FlightGear does not show the bridge.
FG-4.png this is the Southend Pier, the longest Pier in the world at just over one and a quarter miles long, again none existent in FlightGear.
FG-5.png shows a flight over Paris, interesting point here, a lot of the buildings are shown correctly which indicates the technology is there within FlightGear to show urban areas with better detail than the generic overlay.
FG-6.png shows DisneyLand Paris, to be fair, would you recognise that, it is a major landmark.
Once again I reiterate, overall this is a fantastic flight sim, I prefer it over all the other flight sims I have tried. Developing the areas, urban, industrial and commercial to a level that would be recognisable, even as 2D, would dramatically enhance FlightGear. I believe the technology is already there within FlightGear to do that and would provide a better simulation for those of us who fly low altitude and fly by line of sight.
I apologise for the quality for the quality of the pictures as I've had to use the Facebook URL's and Facebook has a habit of reducing the resolution, however you can still see the points that I am making.