My Opinions/Suggestions on the Terrain -
I think a lot of zombie maps leave tons of open space unused by having the building doodads all over which are very large and take up a ton of space. So my suggestion is to instead of having buildings that take up space and are not realistically scaled use an imported wall doodad to create open rooms that players can move into and utilize.
Also making your own tiles or finding tiles will help give a better feel to the game. There are plenty of road tiles and modern city tiles out there.
I think that 256x256 will be much to large for a survival map, even though it sounds like a scavenger style survival map I find that too large of a map leads to drawn out gameplay and overwhelming new players. In my opinion players need to be introduced gradually to a game instead of being dropped right in the middle of it. I would suggest possibly considering taking elements from the popular survival map
Survival 1.357 The main thing I'm talking about is the simple transition from stage to stage with bosses in between, not only does it allow new players to figure things out gradually, but also gives a more defined sense of progression which is for me anyway a great feeling to have my character progressed a lot through out the game.
My Opinions/Suggestions on Survival Games -
I like that you choose to loosely base it off of afterlife because that was a great map. I already mentioned one map that would be good to look at for ideas, but also I think you should take a look at
Mage Seige which did not receive too much popularity, but none the less is a very fun map to play and has great elements similar to Afterlife. A game that may not seem so similar, but I feel could have many cool ideas to draw from is
X Hero Siege although the elements in this map wont be too realistic for the zombie map; adding challenges does not always have to be moving to a different arena and fighting an enemy like in that map, but having bonus quests and objectives that can be taken on by your party will add a lot of depth to a survival game and can be realistic. Also bonus minigames of such would be really cool, but of course make the game a lot less realistic. But diverse gameplay I feel holds the players attention longer.
There are my suggestions. I hope you find them useful.
I respectively disagree.
I think this epic size map is a great idea. Introducing RPG elements makes survival games a lot better, in my opinion. Survival is a good map, but I got bored after a while. Dawn of the Dead was pretty fun and I still play it sometimes but it's missing something. Undead Assault II and SWAT Aftermath were equally fun but they didn't satisfy my thirst either. Let's take a look at some things from those games that made it challenging and enjoyable:
Ranks:
This makes it so players who played often have something to look forward to. They have an attachment to the game that makes them come back and keep playing. Being a Master Sargent level whatever surrounded by a bunch of rookie privates and corporal newbies who are trying the game for the first time gives them some semblance of achievement and pride along with leadership. They worked hard to get that rank and the prestige and benefits that followed.
Perks/Skills/Talents/Classes:
Take every RPG/ORPG out there, they have multiple Heroes with multiple classes. Paladin, Cleric, Warrior, Assassin, Mage. You know why? Because no one wants to play the same goddamn character over and over again. It gets boring, fast. This offers diversity. Classes can be given to players at the start and then later on. Working like a chain of classes, level 1 you pick from three then as you progress in that class, you unlock better ones. (i.e. Soldier --> Veteran --> Juggernaut) or it could be a rank sort of deal. Whereas when you reach let's say level 10, you become a lieutenant and unlock the Scavenger Class or maybe have a choice between a few classes. This heightens the replayability of the map. Perks could be given in an XP style, like you kill 5000 zombies, you unlock the "Marksman" perk and it gives some sort of effect or you Scavenge 300 times and become adept at finding more valuable items.
Items:
Be it edible cheese or a state of the art assault rifle. Items make up a huge portion of any RPG or Survival style map. They're important. It makes the game more fun and everybody loves fighting for them and then flaunting them in other people's faces haha This also extends to a degree of items.
Common Items: Food, Water, Batteries, Monetary Valuables (If present or used) etc.
Uncommon Items: Ammunition, Weapons, Armor, Vehicle Parts, Equipment (Night Vision Goggles, Mines, Gun Parts, Equipment Parts.), Maps, Tools.
Rare Items: Advanced Weaponry and Armor (Laser Weaponry, Plasma Weaponry, Power Armor and equipment.), Advanced tools, Sentry Guns, etc.
This ensures variety and extended fun as it keeps players moving and searching for better gear.
Enemies:
Even zombie killing fanatics get tired of killing the same old zombie. Introduce several types which are REALISTIC and have backgrounds or something describing how the hell they came to being. Maybe enact a quest or have data logs scattered throughout the city providing lore and depth to your map and telling a story of how the hell this world became what it was. The new DLC for Call of Duty: Ghosts has scattered recordings that do this.
Zombie: After the virus was released many of the world's populace were infected and promptly turned into these beasts.
Shambler: Rotting corpses that have survived far past their prime. They are slower but have more health than normal zombies.
Stalker: Fast damaging sprinting zombies that close the distance. However, they trade armor for their speed. Making them weak.
Licker: Highly resilient mutation from the virus, which branched off from the Stalker strain. Fast, high HP and armor. Very deadly.
Dreadnought: Massive beast resulting from speedy mutations and metabolic enhancements.
Swarmer: Fast Zombie but low health, damage, armor. They support other zombies, when they notice a survivor they converge with other masses of zombies essentially becoming one giant Horde.
Just some examples.
This makes it so players have a few weapons with them to counter their enemies during any given situation. Also enhances fun and replayability.
Vehicles:
Always fun, should have something as a challenge before getting them. Be it a quest, a skill, parts to assemble it or a certain class/rank. These shouldn't be OP, if a player get's in a Tank, he should be able to wreak some havoc...for a while, at least. They shouldn't be indestructible. Just fair. A tool to be used, otherwise it just makes them the focus and every player will just rush to use them. They have to be like items or classes or quests. Just an addition to the game that enhances it, not something that dominates it.
Game Modes:
Survival....obviously surviving as long as you can, I'm not really a fan of the whole 'point system' but if that's your kind of thing, go for it. Props to you, man. This should consist of scavenging and working together or against other players. Teams, 3v3 players, working in unison to kill the other team. Campaign/Story Mode, follow a series of quests to uncover why this all started or to repopulate/ensure humanity's survival or just a chain of random ones such as rescuing survivors, protecting a base, rebuilding a generator and then at the end, have a boss fight to give it a climactic ending and XP reward.
Building/Construction:
Let's face it, building your own city is cool as shit. WoW RP, you can be a freelancer or a Warlord (Base Builder). Founders of the North: Base building. It's in a lot of maps and for good reason. This also shouldn't be the focus of the game, just an addition. You can make it so all players have the option to do this or a certain class. Engineer maybe. It makes it a lot more fun to command your own littler area or safezone for other players to occupy in, implement a trading system maybe using old pre-zombie war paper money or just valuables. Make the buildings require building material or supplies.
In Conclusion...
I'm guessing you're trying to make this a very large and fun map. Epic sized and with the systems you've already listed, it says it in itself. These are just ideas and some things I've noticed. This is of course your map and you can do whatever you wish with it. Good Luck, mate. Looks like it's going to be awesome!