UN - Geographic Information Systems
In GIS, a term that refers to the spatial relationships among geographic features (e.g., points, lines, nodes and polygons). A topologically structured database stores not only individual features but also how those features relate to other features of the same or different feature class. For example, in addition to a set of lines representing a road network, the system will store the nodes that define road intersections, which allows the system to determine routes along several road segments. Or, instead of storing polygons as closed loops, where the boundaries between neighbouring polygons would be stored twice, a topologically structured GIS would store each line only once, together with information on which polygon is located to the left and the right of the line. This avoids redundancy and facilitates the implementation of many GIS and spatial analysis functions.
United Nations, "Handbook on Geospatial Infrastructure in Support of Census Activities", Department of Economic and Social Affairs, Statistics Division, Studies in Methods, Series F No. 103, New York, 2009