This usually has to do with your in-game graphic settings. The more you increase the graphic settings the more distance you see. You can’t make it so that ALL players see all of the map because some players will always use a lower graphic settings. Roblox makes lower graphic settings see less distance to decrease lag.
If you have a faster computer you’ll see more, but it’s limited to what Roblox actually allows for their max distance settings. How far in studs do you estimate from your camera to the ‘edge’ of your visible distance showing?
If you have multiple players playing the game they’ll each see as much as their computer will allow. It won’t affect other players.
The thing is, let’s say, if I fly to those “missing” spots I can see even further than before at the same distance from it. So if I fly to the whole map and get back to the beginning, I can see the whole map without any missing spots.
So is there another way of doing it except for flying?
If you search the Streaming Enabled section of the create.roblox.com that @ClearlyVi recommended you’ll see that if Parts are loaded from one section and the player moves to another then the first section Parts may stay loaded depending on the player’s computer performance.