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Topology is a collection of rules that, coupled with a set of editing tools and techniques, enable the geodatabase to more accurately model geometric relationships. ArcGIS implements topology through a set of rules that define how features may share a geographic space and a set of editing tools that work with features that share geometry in an integrated fashion. A topology is stored in a geodatabase as one or more relationships that define how the features in one or more feature classes share geometry. The features participating in a topology are still simple feature classes—rather than modifying the definition of the feature class, a topology serves as a description of how the features can be spatially related.
Topology has long been a key GIS requirement for data management and integrity. In general, a topological data model manages spatial relationships by representing spatial objects [point, line, and area features] as an underlying graph of topological primitives—nodes, faces, and edges. These primitives, together with their relationships to one another and to the features whose boundaries they represent, are defined by representing the feature geometries in a planar graph of topological elements.
Topology is fundamentally used to ensure data quality of the spatial relationships and to aid in data compilation. Topology is also used for analyzing spatial relationships in many situations, such as dissolving the boundaries between adjacent polygons with the same attribute values or traversing a network of the elements in a topology graph.
Topology can also be used to model how the geometry from a number of feature classes can be integrated. Some refer to this as vertical integration of feature classes.
Features can share geometry within a topology. Here are some examples among adjacent features:
- Area features can share boundaries [polygon topology].
- Line features can share endpoints [edge-node topology].
In addition, shared geometry can be managed between feature classes using a geodatabase topology, for example:
- Line features can share segments with other line features.
- Area features can be coincident with other area features. For example, parcels can nest within blocks.
- Line features can share endpoint vertices with other point features [node topology].
- Point features can be coincident with line features [point events].
A layer of polygons can be described and used in the following ways:
- As collections of geographic features [points, lines, and polygons].
- As a graph of topological elements [nodes, edges, faces, and their relationships].
This means that there are two alternatives for working with features—one in which features are defined by their coordinates and another in which features are represented as an ordered graph of their topological elements.
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Topology
In a GIS, spatial relationships among features are defined by topology.
In a geodatabase, you can choose whether to create topology for features. If your analysis will depend on accurately modeling spatial relationships, creating topology is essential. For example, if you are modeling a wastewater network, all the features must be connected or the results of any analysis based on your model will be flawed. Or, if you are calculating the total area for different types of land cover, gaps between land cover polygons will result in inaccurate totals.
There are three types of topology available in the geodatabase: geodatabase topology, map topology, and the topology created for a geometric network. A feature class can participate in only one topology at a time.
Geodatabase topology
A geodatabase topology is a set of rules and properties that defines the spatial relationships you want to model and preserve in your data. ArcGIS includes over 20 topology rules from which you can choose. All feature classes participating in a geodatabase topology must be in the same feature dataset.
A geodatabase topology rule applies to a particular type of spatial relationship. For example, Must Not Have Gaps is a rule that defines a spatial relationship between polygon boundaries.
To create and edit a geodatabase topology, you need an ArcEditor or ArcInfo license.
Map topology
A map topology creates temporary topological relationships among features in one or more feature classes during an edit session in ArcMap. The ArcMap topology editing tools are used to maintain these relationships while editing.
A map topology can be created and edited using ArcView, ArcEditor, or ArcInfo. You'll learn how to work with map topology in Lab 8.
Geometric network topology
In a geometric network, topological relationships are stored in the geodatabase and maintained automatically by the software. In geodatabase and map topologies, spatial relationships are not stored—they are "discovered" as needed [for example, when a feature class is edited in ArcMap]. In a geometric network topology, topological relationships are established between point and line feature classes stored in the same feature dataset.
- Meanings
- Synonyms
- Sentences
Topographic study of a given place, especially the history of a region as indicated by its topography.
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[medicine] The anatomical structure of a specific area or part of the body.
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[math.] The study of those properties of geometric figures that remain unchanged even when under distortion, so long as no surfaces are torn, as with a Möbius strip.
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Topology is the study of the geographic features of a location.
The geographic study of the mountains, peaks and valleys in New York is an example of topology.
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[computers] The arrangement in which the nodes of a network are connected to each other.
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The study of certain properties that do not change as geometric figures or spaces undergo continuous deformation. These properties include openness, nearness, connectedness, and continuity.
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The underlying structure that gives rise to such properties for a given figure or space.
The topology of a doughnut and a picture frame are equivalent.
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A topographical study of a specific object, entity, place, etc.
The topology of the mind.
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[med.] The topographic anatomy of a body region.
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The anatomical structure of a specific area or part of the body.
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The mathematical study of the geometric properties that are not normally affected by changes in the size or shape of geometric figures. In topology, a donut and a coffee cup with a handle are equivalent shapes, because each has a single hole.
[1] In a communications network, the pattern of interconnection between nodes; for example, a bus, ring or star configuration.
The physical and logical structure of a network. Physical topology refers to the physical layout of a network, specifically the physical positioning of the nodes and the circuits that interconnect them. Logical topology refers to the manner in which devices logically interconnect in a network, and may differ considerably from the physical topology. For example, an Ethernet LAN segment may comprise a number of workstations and peripheral devices that interconnect through a hub, with each device connecting directly to a hub port.The physical topology is that of a star, but the logical topology is that of a bus.That is to say that, although the devices connect to the hub over circuits that emanate from the hub like the rays of a star, they interconnect through a collapsed bus, or common electrical path, housed within the hub. LAN and WAN topologies variously include bus, mesh, partial mesh, ring, star, and tree. See also bus, Ethernet, hub, LAN, logical, mesh topology, physical, ring, segment, star topology, tree, and WAN.
[mathematics] A collection Ï„ of subsets of a set X such that the empty set and X are both members of Ï„ and Ï„ is closed under arbitrary unions and finite intersections.
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[medicine] The anatomical structure of part of the body.
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[computing] The arrangement of nodes in a communications network.
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[technology] The properties of a particular technological embodiment that are not affected by differences in the physical layout or form of its application.
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[topography] The topographical study of geographic locations or given places in relation to its history.
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[dated] The art of, or method for, assisting the memory by associating the thing or subject to be remembered with some place.
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