code:

// Dramatically abbreviated code
class Cell
{
  Blocktype[] blocks;
  int height;
}

class Terrain
{
  Cell[,] cells;
  Draw(Spritebatch batch)
  {
    // Determine which cells overlap the viewport
    for (y = yMinTile; y<yMaxTile; y++)
    {
      for (x = xMinTile; x<xMaxTile; x++)
      {
         // Determine which tiles in this cell are visible
         // and only draw those. Ie, if there is a block
         // above and a block in front of this tile, you will never see it
         // so don't render it.
         batch.Draw(cells[x,y].GetTexture(), cellLocationVector, Color.White);
      }
    }
  }
}