A sliver polygon is very long and thin; its perimeter is very large compared to its area. When overlaying two topologies, AutoCAD Map 3D checks for sliver polygons. When creating a new polygon topology, checking for sliver polygons is optional.

If a sliver polygon is detected, AutoCAD Map 3D highlights its centroid with an X. To clear the Xs, use the REGEN command.

Though sliver polygons are not considered errors by AutoCAD Map 3D and your topology can still be considered correct and complete, the sliver polygons may be unintentional, for example, the result of digitizing errors. If you see sliver polygons, you may want to double-check your data to make sure it is correct and that the sliver polygons are expected.

For example, imagine you digitize two adjacent polygons, such as a parcel and a flood plain, and there are slight overlaps between the two. Then, you create topologies for each, overlay the topologies, and the resulting topology contains sliver polygons. These may be correct or not, depending on your data. If the boundaries between the adjacent polygons are meant to be the same, then the sliver polygons are incorrect and you must correct your data. If the boundaries are not meant to be the same, then sliver polygons are correct.

Sliver polygons detected during an overlay (the Xs indicate the sliver polygons).