np.random.rand(city_num, 2)

As an AI language model, I don't have access to the context or previous code. However, I can explain what this line of code does in general.

`np.random.rand(city_num, 2)` creates a 2D array with `city_num` rows and 2 columns, where each element is a random number between 0 and 1. This is often used in simulations or data generation tasks where random data is needed. The `np` prefix indicates that this function is part of the NumPy library, which is a popular library for scientific computing in Python.