One approach to a multilayered map would be an array (or 2-dimensional array) of linked lists or vectors holding tile objects. So your tile struct would either hold a pointer to the next tile above it, or you would have "stacks" of tiles of varying heights spread across the grid. Essentially that creates a 3D array.

A nice, albeit old article on multilayered maps would be here: http://www-cs-students.stanford.edu/~amitp/Articles/Tiletech.html

So for example, your tile struct would look like something along these lines:

struct Tile
    {
    unsigned char type;
    Tile * next = NULL;
    };

The map it self, if for example it was a 2D grid, would look like this:

Tile tile_map[rows][cols];

To then get a tile at a certain point to check whether it collides or not, you would iterate through the list at that point until you reached the desired z position.

unsigned char getTileType(int x, int y, int z)
    {
    //Assuming 0 means an empty (air) tile
    unsigned char tile_type = 0;

    Tile * tile = tile_map[x][y];

    //Iterate through the linked list of tiles  at this position
    int height = 0;
    while (height < z)
        {
        tile = tile -> next;

        if (!tile)
            return tile_type;

        ++height;
        }

    if (tile)
        tile_type = tile -> type;

    return tile_type;
    }

One approach to a multilayered map would be an array (or 2-dimensional array) of linked lists or vectors holding tile objects. So your tile struct would either hold a pointer to the next tile above it, or you would have "stacks" of tiles of varying heights spread across the grid. Essentially that creates a 3D array.

A nice, albeit old article on multilayered maps would be here: http://www-cs-students.stanford.edu/~amitp/Articles/Tiletech.html

So for example, your tile struct would look like something along these lines:

struct Tile
    {
    unsigned char type;
    Tile * next = NULL;
    };

The map it self, if for example it was a 2D grid, would look like this:

Tile tile_map[rows][cols];

To then get a tile at a certain point to check whether it collides or not, you would iterate through the list at that point until you reached the desired z position.

unsigned char getTileType(int x, int y, int z)
    {
    //Assuming 0 means an empty (air) tile
    unsigned char tile_type = 0;

    Tile * tile = &tile_map[x][y];

    //Iterate through the linked list of tiles  at this position
    int height = 0;
    while (height < z && tile)
        {
        tile = tile -> next;
        ++height;
        }

    if (tile)
        tile_type = tile -> type;

    return tile_type;
    }