How can all the nebula be explored if only .02% of the galaxy has been?
Because nebulae are gigantic beacons, attracting explorers like moths to a searchlight. You can see them both in the skybox and on the galaxy map from a long way away.
Check out any of the EDAstro maps of where players have been in the galaxy.
This one, for example. Look particularly at the eastern half of the galaxy. There are very few nebulae out there, compared to the western half of the galaxy, and no known bases or colonies to visit. Do you see all the "hubs", where multiple lines radiate out from? Most of those hubs are going to be nebulae.
Teeny, tiny nebulae - "supernova remnant" class, less than 1 LY across, with a large bright star, neutron star or black hole inside - are hard to spot, and there are probably still plenty of those out there that are Unexplored. But not as many as you might think because people are actively looking for them.
The 99.96% of the galaxy that's still Unexplored is all in "Boring Space", nowhere near nebulae or known human settlements. Most of that's in the Galactic Core, where even the well-travelled routes are still largely Untagged, as the star density is simply so high that hitting an already-explored system is improbable.
This is the exact reason why players should be able to filter stars on the route plotter by which ones have been visited already and which ones have not. Technically, from a coding perspective, I just don't see any real issues - it would be an easy addition to make. From the game logic perspective, it makes zero sense that your navigation computer has been updated with information from stellar cartography that displays the name of who discovered a star without having the ability to show you before you get there if it has been visited already. The lack of this feature confuses me; No downside to having it as a feature and no upside to it being left out.
This is an easy one: FD simply don't
want to make it easy for explorers to know which systems have been explored and which haven't. You're supposed to go out there and look for yourself. It's much the same logic as trade data: if you've never been there, you don't know what prices they're offering. You have to travel there yourself and look - even though in a real-universe situation, a rarely-visited star system would be shouting its buy/sell prices across the galaxy, in order to attract customers.
Evidence for it being a deliberate policy: back when I started playing the game, inhabited star systems were divided into two categories: Explored and Unexplored. Explored systems were those that had a population over 1 million. With Explored systems, you could open up the System Map and look at the stars and planets present,
even if you'd never been there. Then they introduced Mapping, and players could suddenly acquire new Tags all over inhabited space, even in Explored systems. What did FD do? They
withdrew system map viewing privileges for Explored systems you had not yet visited. This means that you can't "armchair explore", from the safety of your docked spaceship, to find planets in nearby systems that are not Mapped yet - you had to launch your spaceship, travel there and look. FD did not want to make it that easy for players to find Unmapped planets within the Bubble. The result: until a few months ago, there were still a few rarely-visited star systems within the Bubble with Unmapped planets in them. I found and mapped several of them, less than a year ago; the
Guo Zi system was an example I posted here on the forum back in April 2020, as an experiment (those planets were Mapped within a day of my making the post). A
systematic effort by a group of players to Map the entire Bubble is still finding about a dozen Unmapped moons per week.
If FD had an at-your-fingertips map of Unmapped worlds, all those worlds would have been Mapped within an hour of Mapping going live, and the nearest Unmapped world would probably be 6000 LY away.
There are approximately 400,000,000,000 stars in our game galaxy - (or possibly 400,000,000,000,000 as it depends on which 'billion' has been adopted) which would explain why such a small number is being quoted as 'discovered' to date.
It's the smaller one, the "short-form" or the "American billion". It's the same "billion" that we use when we say, "There are 7.6 billion people on Earth in 2020".