以北

1. Origins, structure, and basic meaning

• Structure: 以北 is read as いほく and marks the area north of a stated reference point or boundary such as a river or station.
• Basic usage: Attach it directly to the reference in 川以北が保護区域 or 駅以北の路線.

2. Common pitfalls and similar expressions

• Direct attachment
  • The reference noun joins directly as 川以北 or 駅以北, without inserting の.
• Difference from 北
  • 北 names the direction itself, whereas 以北 defines a region extending northward from a specified reference.