5.2 Geodatabase Datasets & Structure

5.2 Geodatabase Datasets & Structure

Organizing spatial and tabular data inside an Esri geodatabase requires a firm grasp of hierarchical data containers, spatial reference rules, geometry types, and data integrity mechanisms. ArcGIS Pro provides a flexible structural framework that enables GIS analysts to model real-world spatial entities while enforcing strict data validation. This section explores the architectural components of geodatabases, focusing on Feature Datasets, standalone feature classes and tables, Attribute Domains, and Subtypes.

Feature Datasets and Spatial Reference Rules

A Feature Dataset is a specialized thematic container stored inside a geodatabase used to group feature classes that participate in shared topological or network relationships. Feature datasets are required when creating advanced geodatabase structures, such as Geodatabase Topologies, Utility Networks, Trace Networks, Network Datasets, and Parcel Fabrics.

The Spatial Reference Requirement

The fundamental rule governing Feature Datasets is spatial reference uniformity: every feature class contained within a single Feature Dataset must share the exact same spatial reference. This includes:

• Horizontal Coordinate System: Map projection and geographic datum (e.g., NAD 1983 State Plane Texas Central, WGS 1984).
• Vertical Coordinate System (VCS): Optional elevation datum (e.g., NAVD88).
• XY Tolerance and Resolution: Numerical precision settings defining the minimum distance between vertices before they are treated as coincident.
• Z and M Tolerances/Resolutions: Precision parameters for 3D elevation (Z) and linear referencing measure (M) values.

When a user creates a new feature class inside an existing Feature Dataset, ArcGIS Pro automatically enforces spatial reference inheritance. The new feature class inherits the spatial reference of the parent Feature Dataset, prohibiting the user from altering coordinate systems or tolerance settings for that feature class. If datasets with differing spatial references must coexist in the same geodatabase without participating in topology or networks, they must be stored as standalone feature classes.

Standalone Feature Classes and Geometry Types

A Feature Class is a homogeneous collection of spatial features with the same geometry type and attribute schema. Features within a feature class represent real-world geographic entities (such as fire hydrants, roads, or parcel boundaries) and are indexed by a unique OBJECTID primary key field.

ArcGIS Pro supports four primary vector geometry types for feature classes:

1. Point: Single-coordinate pair (X, Y) representing discrete zero-dimensional spatial locations (e.g., utility poles, tree inventories). Points can optionally include Z (elevation) and M (measure) values.
2. Multipoint: A single feature composed of multiple spatial point coordinates. Multipoints are used to store dense collections of point data (such as LiDAR ground returns or weather station clusters) where managing millions of individual point rows would degrade performance.
3. Polyline: One-dimensional linear geometries composed of connected vertices forming segments and paths. Polylines represent linear networks (e.g., rivers, roads, pipelines) and can be single-part or multi-part.
4. Polygon: Two-dimensional enclosed areas defined by boundary rings. Polygons store areal features (e.g., land parcels, zoning districts, lakes) and support multi-part geometries with interior holes (donut polygons) or island chains.

Standalone Tables

A Standalone Table is a non-spatial attribute table stored directly inside a geodatabase. Like feature classes, standalone tables contain rows and columns and automatically include a system-managed OBJECTID field. However, standalone tables contain no shape column or spatial coordinate data. They are used to store lookup information, business tabular records, or historical logs that link to spatial feature classes via joins, relates, or relationship classes.

Attribute Domains

Attribute Domains are rules that define valid values for field attributes in a geodatabase table or feature class. Domains operate at the geodatabase level; once created, a single domain can be applied to multiple fields across different feature classes and tables within that geodatabase. By restricting data entry to valid values, domains eliminate typos, enforce data standards, and enhance editing efficiency during field collection and desktop digitization.

ArcGIS Pro supports two distinct types of Attribute Domains:

1. Coded Value Domains

Coded Value Domains define an explicit, discrete list of acceptable values for an attribute field. Each entry consists of a Code (the actual value stored in the database disk file, often an integer or short string) and a Description (the human-readable text string displayed in attribute tables, pop-ups, and drop-down editing menus).

Example: A coded value domain named PipeMaterial might store integer code 1 for Description 'Ductile Iron', code 2 for 'Polyvinyl Chloride (PVC)', and code 3 for 'Concrete'.

2. Range Domains

Range Domains specify a permissible minimum and maximum numeric or date boundary for a field. Any value entered outside the defined range is flagged as invalid during attribute validation. Range domains can be applied to short integer, long integer, float, double, and date field types.

Example: A range domain named OperatingPressure applied to a water main feature class might set a minimum valid value of 20.0 PSI and a maximum valid value of 150.0 PSI.

Subtypes

Subtypes are subsets of features within a single feature class (or rows in a table) that share common characteristics. Subtypes are implemented by designating a specific short or long integer field within the feature class as the Subtype Field. Each integer value in the field represents a distinct subtype category.

Benefits and Operational Advantages

Instead of creating separate feature classes for closely related real-world entities (e.g., separate feature classes for Local Roads, Arterials, and Highways), a GIS architect creates a single Roads feature class and uses an integer RoadType field to define subtypes (1 = Local, 2 = Arterial, 3 = Highway).

Subtypes allow GIS managers to customize the following properties per subtype within the same feature class:

• Default Values: Assign unique default field values for each subtype (e.g., default speed limit of 25 mph for Local Roads vs 65 mph for Highways).
• Domain Bindings: Apply different Coded Value or Range Domains to the same field based on subtype (e.g., applying a lower pressure Range Domain to residential water mains and a higher pressure domain to commercial mains).
• Topology Rules: Enforce distinct spatial rules per subtype within a Geodatabase Topology.