You can convert all, or a selection of, the closed polylines in an existing drawing to polygon objects. When you convert a closed polyline, the original polyline is erased and is replaced with a polygon object.
This illustration shows a map made of polylines. Every closed polyline is converted to a polygon.
This illustration shows a state with lakes as closed polylines.
To create a complex polygon with islands, holes, or discontinuous polygons, first use the GROUP command to group the objects that you want to include in the polygon. Then use the MAPPOLYLINETOPOLYGON command.
To preserve nested data, you may want to convert your polylines in steps. For example, in the illustration above, you could first query in the state and lake boundaries, group all these objects, and create a polygon. The resulting polygon will show the state with holes for the lakes, and will maintain only the state data. Next, query in the lake polylines, do not group them, and then convert the lake polylines to polygons. Each of the polygons representing the lakes will have its data attached.