def plot_population(ax, population_coordinates):
    """Plot 3D population.

    Arguments:
        ax: ax
        population_coordinates: coordinates of the population

    """
    X = [x for x, y, z in population_coordinates]
    Y = [y for x, y, z in population_coordinates]
    Z = [z for x, y, z in population_coordinates]
    points_on_the_plot = ax.scatter(X, Y, Z, s=1, c="black")

    return points_on_the_plot