IArea Interface

Provides access to members that return properties common to rings and polygons.

Available with ArcGIS Engine, ArcGIS Desktop, and ArcGIS Server.

Use the IArea interface to get the Area of a Geometry. It can also be used to get the Centroid point and Label point for a Geometry.

		Description
	Area	The area.
	Centroid	The center of gravity (centroid).
	LabelPoint	A point guaranteed to be inside this area.
	QueryCentroid	Copies the centroid of this area to the specified point.
	QueryLabelPoint	Copies to the input point a point guaranteed to be inside this area.

CoClasses and Classes	Description
Envelope	A rectangle with sides parallel to a coordinate system defining the extent of another geometry; optionally has min and max measure, height and ID attributes.
GeoEllipse (esriMilitaryAnalyst)	A spheroidal ellipse.
GeoPolygon (esriMilitaryAnalyst)	A spheroidal polygon.
MultiPatch	A collection of surface patches.
Polygon	A collection of rings ordered by their containment relationship; optionally has measure, height and ID attributes.
Ring	An area bounded by one, closed sequence of connected segments; optionally has measure, height and ID attributes at each vertex.

EDN: ESRI Developer Network