practical halachos learned from the description of cities of the Levi'im

The specifications of the boundaries of the cities reserved for Levi'im may not seem of much contemporary halachic interest, but some basic laws of Eiruvin are derived from that parsha. Thumbing through Mishnayos Eiruvin will get you at least two of them. Curious? Take a look at 4:8 and 5:2 (you didn't expect me to do the work and write out the halachos, did you? : )