Definition of observation space

[locker2153]

I have some questions about the value range of the observation space represented by spaces.Box.
Why is it set like this?
“
low=np.zeros(self.ts.num_green_phases + 1 + 2 * len(self.ts.lanes), dtype=np.float32),
high=np.ones(self.ts.num_green_phases + 1 + 2 * len(self.ts.lanes), dtype=np.float32),

”
How do I understand it?
num_green_phases + 1 + 2 * len(self.ts.lanes)

class DefaultObservationFunction(ObservationFunction):
"""Default observation function for traffic signals."""

def __init__(self, ts: TrafficSignal):
    """Initialize default observation function."""
    super().__init__(ts)

def __call__(self) -> np.ndarray:
    """Return the default observation."""
    phase_id = [1 if self.ts.green_phase == i else 0 for i in range(self.ts.num_green_phases)]  # one-hot encoding
    min_green = [0 if self.ts.time_since_last_phase_change < self.ts.min_green + self.ts.yellow_time else 1]
    density = self.ts.get_lanes_density()
    queue = self.ts.get_lanes_queue()
    observation = np.array(phase_id + min_green + density + queue, dtype=np.float32)
    return observation

def observation_space(self) -> spaces.Box:
    """Return the observation space."""
    return spaces.Box(
        low=np.zeros(self.ts.num_green_phases + 1 + 2 * len(self.ts.lanes), dtype=np.float32),
        high=np.ones(self.ts.num_green_phases + 1 + 2 * len(self.ts.lanes), dtype=np.float32),
    )