Wireless networks, such as Wi-Fi, 2G, 3G, 4G and WiMAX, whether governed by standards or proprietary protocols, often overlap with one another. Multiple wireless networks of the same type, perhaps with configuration-specific differences, also often overlap with one another.
A wireless device chooses an available wireless network to associate with. The choice is generally made based on user selection, whether or not a better selection is available for a given situation.