Some advice for settling on a map format for a tile game?

5) Don't roll your own. .NET in general has really great serialization functions, and XNA is no exception: http://msdn.microsoft.com/en-us/library/bb203924.aspx

Edit: As far as WHERE to store them, they should be resources in a class library, and however you serialize your data should refer to them using reflection (I typically also have some sort of easier to use string alias as well, because reflection names are ugly).

Somehow mention the directory or filename of the tileset from within the text map file. This is how I typically see it done, but because I am using the content loader and not simply loading off the hard drive, this may not be possible. Perhaps the asset name could be stored but this solution seems a bit error-prone.

Check out the ExternalReference class. You can load an external Texture2D by its file name relative to the location of the file currently being processed. So as long as the text file that stores the tile data stores the location of the tile map you are good to go.

In my game I have several layers of tiles to achieve the parallax effect. Each layer is a 2D array of a minimal Tile class. If the array element is null, there is no tile there. The tile class stores an enum that refers back to a tile template class, which might be Lava or Wall, or Grass, etc. The template tells me all of the attributes that tiles of that kind share, like what the texture & u,v coordinates are, whether it's walkable by default, what its vertex colors should be. In your case this might also include what music should be playing. The individual tile objects in my layer array can override the template values to do something interesting. All the tiles in a layer use the same texture atlas so rendering them is just one batch but you could just as easily use multiple textures. My layer texture is loaded by the ContentManager and assigned to the layer when my level initializes. When drawing, I interleave the layers with the game objects (characters, monsters doors, chests) that occupy each layer for some simple occlusion.

Unless I misunderstand, you are asking how to make a 2D tile engine. This tutorial will walk you through the process, among other things.

Most developers do not solve this problem. They use an existing tile engine. Several exist for XNA.

If you feel compelled for some reason to make your own, I think the best option would be to have a Tileset object, then have each tile know its tile code, and have the draw method look at each tile, get its code, get that code's tile graphic from the tileset and draw.

As for specifying a tileset, it should be enough for each map to specify a tileset code, and the the Tileset object can fetch the relevant tile sheet for that code.

In any event, the thing you appear to ignore is: You should find a map editor you can use, and then code such that you are compatible with it, thereby saving yourself the trouble of writing your own editor later. The way the map editor does will probably immediately suggest simple answers for your questions.