Model answer

AOI = Area of Interest. It’s like cropping a satellite image down to just the patch you care about. Could be a polygon, a rectangle, or a weird outline — whatever fits your study area.

Why bother? Two reasons:

• Speeds things up — the computer only crunches the area you specified, not the whole 185 km × 170 km Landsat scene.
• Keeps your training samples honest — you don’t want unrelated land-cover muddying your stats.

In ERDAS Imagine you draw it on the screen and the software respects it for whatever you do next.

🔬 Show the science / technical version

• User-defined spatial subset — polygon, rectangle, or irregular shape.
• Restricts an operation to part of an image (clip, classify, summarize stats for only that area).
• In ERDAS Imagine, an AOI can be one region or a layer of regions.
• Why: saves processing time + disk space, and focuses training statistics on the intended target.