Prayer: The Permitted Limit for Elevated or Depressed Towns and Roads
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 1306
If a town’s location happens to be elevated such that its residents can be seen from around it, or if it happens to be in a depression such that if one went a short distance away from it he would not see its residents, then, if a resident of that town travels and reaches a distance such that had the town’s location been at ground level he would not be able to see its residents, he must perform qaṣr prayers. Similarly, if the elevation or depression of the road he is travelling on is more than normal, he must take into account a normal type of road [in determining whether he must perform qaṣr or tamām prayers].