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Topology

Topology?

Topology can be understood as the "rules of spatial behavior" that govern how geographic features relate to one another in a GIS environment. It defines the logical relationships between points, lines, and polygons, transforming a simple digital drawing into an intelligent and analyzable spatial network. Without topology, GIS data remain visually correct but analytically unreliable.

1️⃣ Adjacency (The "Jigsaw Puzzle" Rule)

Concept: Adjacent polygons must fit together seamlessly.
Rule: There should be no gaps (slivers) and no overlaps between neighboring polygons.
Example: Two adjacent land parcels must share a single, common boundary. A parcel cannot overlap another parcel, nor can empty spaces exist between them—just like pieces of a jigsaw puzzle fitting perfectly.

Connectivity (The "Plumbing" Rule)

Concept: Line features must connect properly at nodes to form a continuous network.
Rule: Lines must connect end-to-end, with no undershoots (lines stopping short) or overshoots (lines extending beyond a junction).
Example: If a water pipeline on a map stops even a small distance before reaching a valve, the GIS interprets it as a broken connection. As a result, network analyses such as flow or routing will fail.

 Containment (The "Box" Rule)

Concept: Certain features must be located entirely within other features.
Rule: One feature must lie inside another feature when required by spatial logic.
Example: A school represented as a point must be located within the boundary of its designated education district polygon—not outside it.


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