We describe a method for populating large virtual environments with crowds of virtual pedestrians. Pedestrians are distributed in the environment by giving them goal destinations to reach. In order to facilitate this population setup, we assign identical destinations to batch of pedestrians, resulting in navigation ows. In order to preserve individuality of pedestrians, navigation is planned with variety and each pedestrians follows its own unique trajectory. This specic navigation planning technique answers user's queries very rapidly. As a result, impact of the insertion of a new navigation flow in the environment is directly observable, and interactive design is achieved. Once the problem of design solved, we address the problem of simulating the virtual population navigation. A level-of-details strategy is used to achieve on-line real-time simulation of large crowds, formed by up to tens of thousands of pedestrians. We illustrate our method on the typical example of a virtual city, and discuss our approach.