public void draw(Graphics2D g)
    {
        int half_block = (int) (block_size*0.5);
        for(int j = 0; j < grid[0].length; ++j)
        {
            for(int i = 0; i < grid.length; ++i)
            {
                if(grid[i][j].size() > 0)
                {
                    Observation firstObs = grid[i][j].get(0); //grid[i][j].size()-1
                    //Three interesting options:
                    int print = firstObs.category; //firstObs.itype; //firstObs.obsID;
                    g.drawString(print + "", i*block_size+half_block,j*block_size+half_block);
                }
            }
        }
    }