The main difference with the railgun is that it's a long range weapon. It changes a lot of things which you can observe best on Lost World where it is not present.
Playing the long distance game is something that especially out of control players profit from as they can keep position while being able to prevent the opponent from gaining stack infinitely (if you know item timings it's easy to hit a rail from a distance; that gets a lot harder with LG or RL depending on the map geometry).

Good aimers can use the rail very offensively too. It also depends a lot on the map (e.g. rail on aero has an entirely different meaning to it as it is very important for the in control player to deal damage on the freshly respawning opponent and because the map offers a lot of angles). However, due to the noise the RG makes and the long reload time it can be risky to use it for attacking. Missing a shot can cost you a lot of stack if you don't act smart.

How does it affect map design? Generally you want to lay out your map geometry to give every weapon a purpose while not making one of them overpowered (that's also part of the reason why aerowalk is boring in QL). Again, you can observe that very well on Lost world where you need LG to be able to compete in the open yard and RL to not get raped in the tight corridors. The weapons work much like powerups here. Denying either LG or RL you can really make it hard for your opponent.
If railgun is there too; generally I would say players have a harder time maintaining control because they can't deny weapons as easily. You could say railgun adds some kind of imbalance to the Ying-Yang of LG and RL which out of control players can profit from. In the end it's a demand/offer sort of thing. You have more weapons on the map so having one particular weapon is a little bit less important on a basic level. Obviously, you can position yourself more effectively if you have all of them - that's out of question.

You can observe a simular happening on tourney4 (vertical venegeance) where there is only RL and RG. There is a focus on denying rail that other maps don't have in the same fashion.
On Campgrounds you can often guess or know your opponent might be going to rail but there is by far not the same focus although the weapon is highly import for out of control play on the map.

Would you say that RG promotes or suggests certain map characteristics, such as larger, more open areas? I'm talking about what the designer thinks as he creates a map including RG.

Certainly it adds a big item to the map, which would help populate a large map with items and make that item layout more dynamic.

Defenitely but you would find most maps that have rail to be working without it while not all maps that don't have rail would work with it. What that tells us is probably the opposite of what you were guessing. The absense of rail allows key areas to be more open if there is a good range of tigher areas to compensate.

The reason is rather simple; LG = hitscan, mid range + RG = hitscan, mid/long range while RL = projectile,short range or mid range if you are pretty good at this game.
So with LG and RL on a map the ratio of hitscan/projectile weapons is 1. If there is rail too, the ratio turns to 0.5 which means mid range fights are more likely to be taking place IF the map geometry does not compensate for it. Consequently the map can not rely as much on open areas or it will turn into an aim festival. This is a quite bold and simplified statement which could quite certainly be argued about but it's good enough for a basic idea.

That's also why the HMG was such a bad idea. It's easier to aim with than LG but in the end it adds even more imbalance to the projectile/hitscan weapons ratio which is why the game does actually get more aim heavy instead of less.

Regarding your second paragraph: You don't build rooms and then add weapons to them when creating a map but add weapons first and then think about how to wrap it so it works.

more weapons mean a larger map, that's what i was suggesting.

I hear what you're saying about item layout being more important than map geometry, or coming first. But I've been thinking about it and I disagree. Are you suggesting that the first step is to place a bunch of items in space? I don't think geometry is inferior to layout, they are both important and they affect eachother.

Saying, I want two rocketlaunchers, one high and one low, separated by about 2000 vertical units. I want one lg at about 800 units height, and within 1000 units of the low rocket on the xy axis. Now I have to think of which geometry to use to connect these items.
This sounds fucked up to me.

Why can't I create a room or area, with available weapons and items in mind? If I know I'm going to put an lg in my map, even if I don't know where, I can create a room with lg in mind. I can say, I want the player to be able to shoot lg from one corridor to another at max range. I can set a midair tele exit to make that tele more dangerous to use. And I can do these things without knowing where I am going to put my lg.

I love QW, its a perfect game on its own. Yet i think rail adds a depth that in QW is void, in QW if you see your oponent from very far distance, basically nothing happens otherwise than the info both players now have of the other player position. On quakelive, when players see each other at long range, if only one player has rail, hes at clear advantage, not only that but long range becomes so important that a really good rail player can win vs an inferior rail player by abusing long range.

This coming from a player that prefers playing and specting +forward, aggresive styles or balanced ones, heavy +back rg players bore me and i end losing vs players with such style mostly because of that reason. Example when theyre confident in the last two or one minutes due to frag difference and engage in med to close combat, im able to make many consecutive frags.

Oddly, rail hasn't scared me in years. I kinda expect my opponent to hit every rail. If they don't switch to a better weapon, they are going to die. Rail has been nerfed to shit basically. Fucking rockets though.

Rail scared me in q2 :P

Q2 weapons were kinda awesome, but starting with blaster was kinda shit. Also the delay in firing the rail kinda added to the skill it was needed to use it.

I believe that spawning with blaster is good actually, it suits the balanced weapons of q2, the blaster can be powerful if you try hard enough, spawning with mg in q2 would be a failure imo.

As for me RG is a king, because RG has fast reloading speed and easy to aim.

easy to aim yes, fast reloading? wut?

Yes, fast reloading, because missed shots from RG is hard to punish, but -80hp always guaranteed. Obviously, RG is offensive weapon in QL, you can use RG in any situation, abuse like no other weapon in QL.

QW don't need RG at all. Gameplay are totally different without any "sniper weapon".

At least Q2 RG + QW RL/LG/GL must be good formula for new Quake.

I would rather the RG take off much less damage, I think it takes a lot of the fun and skill out of the core game.

its needed, but should you get so much reward for virtually no risk?

No.

Or if they keep it, maybe some kind of self damage radiation charge applied to it, so when you have it whipped out, the story behind it is the uranium slugs are hurting you.

Just slowly, just something to change peoples mindset about using it all the time.

After update than LG was nerfed to 6, RG/LG combo still most effective and popular in QL, but who give a fuck about RL...

Wow... I put this discussion away a long time ago.

At this point in time there's no argument that the rail gun or a weapon like it plays a role in deathmatch. It really comes down to map design. A map designer can choose to make a non-railgun or railgun map.

As a competitive gamer it's to take advantage of the items given to you and maximizing your strengths. Railgun is not just about aim... it's also about positioning.

GLHF