Translation guide
In Japanese, expressing 'horizontal plane' depends on context: geometry, everyday flat surfaces, or technical fields. The most common term is 水平面 (suiheimen) for a level surface, while 平面 (heimen) refers to a flat plane in mathematics or design. For physical horizontality, 水平 (suihei) is often used as a noun or adjective.
horizontal plane (geometry)
horizontal plane (level surface)
A flat, two-dimensional surface extending infinitely in all directions, often in math or physics.
A physically flat, level surface like a tabletop, floor, or ground.
Common for any level surface, from tabletops to construction.
Please place the cup on the horizontal surface of the table.
Often used as a noun meaning 'horizontal' or 'level', can imply a horizontal plane in context.
Literally 'flat surface', a more colloquial way to describe a horizontal plane.
In fields like architecture, surveying, or aviation, referring to a horizontal reference plane.
平面 (heimen) is a general flat plane, not necessarily horizontal. 水平面 (suiheimen) explicitly means a horizontal plane. Use 水平面 when levelness is important.
In casual conversation, 平らな面 (tairana men) or simply 平らなところ (tairana tokoro) is more natural than technical terms.
Specifically a horizontal plane, often in physics or engineering contexts.
The object is sliding on a horizontal plane.
この板は水平が取れていない。
This board isn't level.
Please work on a flat surface.
Measure the height from the horizontal datum.