Here's my issue.
I need an efficient way to save, load and compress mapdata during the game (on-the-fly).
I normally use simple *.txt files for my 2D maps but i don't want to make a txt file for every floor of the map
In addition the maps will get quite big and i dont know if an array would be the right way to handle it in my program.
As i said the maps will get big and i assume that there will be many maps, so i want to compress them.
(And maybe later make it harder to edit from outside)

I think the map would consist of tile ids.

So:
a)How do i save a 3D map so that i can easily edit it ( 1 tile instead of the whole map)
b)How do i store/use it in my program. Array?
c)How could i compress the map file. Like RLE

Lots of options are available.

a)
What is wrong with having several files for one map, eg in a directory? Is great for debugging/testing.
For users it is less convenient, but you can use a zip or tar format to pack it into a single file.

I see no particular reason why you cannot have several floors in a single text-file either, can you elaborate why that is a bad idea?

b)
That really depends on the game. if it is all fixed size, array would be fine. You can also do it vertically, a stack at each tile position.
I would decouple the problems of map representation in a file and in memory completely, they are totally different problems with different characteristics and requirements.

c)
Use a compression algorithm that compresses the data stream on writing (and decompresses on loading).
Eg the gzip library does that.
Basically, you have a function/object that you call for each byte that you write, and the function/object decides what to write to the disk (if any). It also updates its internal administration to keep track what decisions it made in the past.

Do you really need this or do you just think you need it?

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