polygonization

Polygonization is the process of forming polygonal features from a set of linework or raster data. In geographic information systems (GIS), polygonization converts a network of line features that delineate boundaries into closed polygonal regions. It relies on the topology of a planar graph: edges form closed rings that bound faces, which are then turned into polygon features with attributes derived from the input data. The process is fundamental for creating area-based layers such as land parcels, political boundaries, or land-use zones from a set of lines that delineate borders. Practical challenges include gaps, overlaps, dangles, and topological errors; preprocessing steps such as snapping, dissolving, and validation are often required to produce valid polygons.

Raster-to-polygon conversion is another form of polygonization, where an image or gridded data set is converted into vector polygons by tracing the boundaries between regions of homogeneous values. This is common in cartography, remote sensing, and image analysis, sometimes followed by simplification and generalization to reduce vertex count.

In computer graphics and geometric modeling, polygonization refers to constructing polygonal meshes from sampled data or implicit surfaces. Techniques include marching cubes, marching squares, and surface reconstruction methods such as Poisson reconstruction or alpha shapes. The resulting polygon meshes are used in visualization, finite element analysis, and 3D printing.

Polygonization raises issues of topology, accuracy, and performance, particularly with large datasets or noisy inputs. Evaluation often involves checking polygon validity, area computation, and alignment with real-world boundaries.