Overlay of vector data is a little bit complicated because it must update the topological tables of spatial relationships between points, lines and polygons.

Overlay of vector data results in the creation of new line and area objects with additional intersections or nodes, that need topological overlay.

There are three types of vector overlay.

point in polygon overlay: points are overlaid on polygon map as shown in Figure 4.7 (a). Topology of point in polygon is "is contained in" relationship. Point topology is a new attribute of polygon for each point.

line on polygon overlay: lines are overlaid on polygon map with broken line objects as shown in Figure 4.7 (b). Topology of line on polygon is "is contained in" relationship. Line topology is the attribute of old line ID and containing area ID.

polygon on polygon overlay: two layers of area objectives are overlaid resulting in new polygons and intersections as shown in Figure 4.7 (c). The number of new polygons are usually larger than that of the original polygons. Polygon topology is a list of original polygon IDs.