How to spawn in loop like snail but in square

Question

Hello I am French so excuse my bad English please, I created a generation of land with a seed with prefabricated gameobjects but they spawn from column to column so I would like to create this but starting from the center to outside like a snail but in square

I partially succeeded, the first image shows the generation in columne but also the desired final result with the generation in snail and the second shows what I managed to do therefore in snail but my pieces of land are square it looks bad

• First:
  
• Second:
  
• It works like:
  
• And I want it Work like:
  

Answer 1

Let's assume you start from the origin O and the other 4 directions are E,S,W,N

  N
W O E
  S

Then the step sequence you'll move is

E S
W W N N
E E E S S S
W W W W N N N N
...

You may notice that every time you turn twice, you need to increase the number of times you move in this direction by one.

Some pseudocode:

var dirs = new Vector3[] { E, S, W, N } // 4 directions
Vector3 pos = O; // origin

do
{
    var dir = 0
    var moveTimes = 1

    for (i = 0; i != 2; ++i)
    {
        for (j = 0; j != moveTimes; ++j)
        {
            pos += dirs[dir]; // step forward
        }
        dir = (dir + 1) % 4; // turn
    }

    moveTimes++;
}
while(/* condition to stop */);