AOI (Area of Interest) is a user-defined spatial subset — a polygon, rectangle, or irregular shape — that restricts an operation to a portion of an image. In ERDAS Imagine, an AOI can be a single region or a layer of regions and is used to clip, classify, or statistically summarize just that area.

• Why: saves processing time and disk space, and keeps training statistics focused on the intended target (e.g., only the agricultural valley, not the whole scene).