<b>Definition.</b><br/>Zones which are physically marked, and which can be visually identified by humans. They have a permanent character.<br/><br/><b>Remark.</b><br/>Applied in Greenhouses.<br/><br/><b>Examples.</b><br/>Painted surfaces<br/>Beds in a field<br/>rows of plants in a greenhouse<br/>rows of trees in an orchard.<br/>