A GIS integrates information about various geographic and nongeographic entities, many of which can be related.
- Geographic entities can relate to other geographic entities. For example, a building can be associated with a parcel.
- Geographic entities can relate to nongeographic entities. For example, a parcel of land can be associated with an owner.
- Nongeographic entities can relate to other nongeographic entities. For example, a parcel owner can be assigned a tax code.
The ability to relate nongeographic (nonspatial) data to geographic (spatial) data is important for several reasons such as the following:
- It enhances the understanding of spatial features beyond their physical location or shape. For example, a point on a map could represent a city, but when you attach nonspatial information such as population, gross domestic product (GDP), or climate data, you gain a much richer understanding of that city.
- It allows for more sophisticated analysis. With associated nonspatial data, you can perform demographic analysis, environmental modeling, economic forecasting, and more.
- It aids in decision-making. Planners, policymakers, and businesses can use this integrated information to make informed decisions about resource allocation, infrastructure development, and risk management, to name just a few.
ArcGIS Pro provides several ways to associate features and records with each other in a geodatabase using both nonspatial and spatial relationships, which are described in greater detail in the following sections.
Nonspatial relationships
Nonspatial relationships in ArcGIS Pro are based on common attributes in the attribute table of datasets. They can be used to model interactions that are not based on geographic location. Click the links below to learn more about each of these nonspatial relationships.
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Join—A join appends the attributes of one dataset to another based on a common attribute field. The result is a new, temporary table that is typically used for data analysis or map symbolization. For example, you might join a table of demographic data such as population to a layer of state boundaries based on a common State_ID field, or you might have a dataset of cities with a City_ID field, and another dataset of population data with a corresponding City_ID field. An attribute join can associate these datasets based on the City_ID value.
Relate—A relate can be used to temporarily associate records between two tables based on a common attribute field. Unlike a join, a relate does not append the attributes of one table to another, but instead allows you to access related data on a record-by-record basis. For example, you might relate a table of parcels with a table of owners based on a common parcel ID, or if you have a layer of cities and a table of annual rainfall data for those cities, you could create a relate to view the rainfall data for each city.
Relationship class—A relationship class is a more advanced type of nonspatial relationship that can be used to model complex relationships and interactions between tables. A relationship class is a dataset type in the geodatabase that permanently stores the relationship between features in one table and features in another. For example, a relationship class could be used to link a table of properties and a table of owners, where each property is associated with one owner, and each owner can be associated with many properties.
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Attachments—Attachments are a way to associate files (such as images or documents) with specific records in a geodatabase. For example, you could have a layer of historic sites, and each site could have an attachment of a photo of the site.
See data relationship options to explore and learn more about joins, relates, and relationship classes.
See data relationship comparison to access a table matrix to help you decide which data relationship option to use.
Spatial relationships
Spatial relationships in ArcGIS Pro are based on the geographic location of the features in the datasets. They can be used to model the way geographic features interact with each other. Click the links below to learn more about each of these spatial relationships.
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Spatial join—This is a special type of join in which features are associated based on their spatial relationship rather than a common attribute. For example, you could use a spatial join to associate a layer of points representing crime incidents with a layer of polygons representing police districts, where each point is associated with the district it falls within.
Topology—Topology in a geodatabase defines the spatial relationships between features in a dataset. Topologies are a set of rules and behaviors that model how points, lines, and polygons share coincident geometry. They are used to define and enforce spatial data integrity rules, such as 'polygons must not overlap' or 'lines must not have dangles' for features in a geodatabase. A topology class in a geodatabase is a collection of these rules and behaviors that describe how features share geometry. Parcel fabrics, network datasets, trace networks, and utility networks are just a few examples of datasets in ArcGIS Pro that use a form of topology to model spatial relationships between various features.