What are Feature Classes?

Definition

A feature class is a collection of geographic features that share the same geometry type (such as point, line, or polygon) and the same attribute fields for a common area. Examples: streets, well points, parcels, soil types, and census tracts etc. A feature class can contain only one kind of geometry—point, line, or polygon and should have unique names. Feature classes can be stored in several different formats. Some formats contain only one feature class, whereas some store multiple feature classes and are called feature datasets.

Basic Rules

  • There are some basic rules that you need to follow while creating feature class.
    • Names must begin with a letter, not a number or special character such as an asterisk (*) or percent sign (%).
    • Names may not contain spaces. If you have a two-part name for your table or feature class, connect the words with an underscore (_), for example, garbage_routes.
    • Names should not contain reserved words, such as select or add. Consult your DBMS documentation for additional reserved words.
    • The length of feature class and table names depends on the underlying database. The maximum name length for file geodatabase feature classes is 160 characters.

Types of feature classes. (Reference)

  • In general, feature classes are collection of geographic features that share the same geometry type (such as point, line, or polygon) and the same attribute fields. But there are more feature classes types that we need to know about:
    1. Points: Features that are too small to represent as lines or polygons as well as point locations (such as GPS observations).
    2. Lines: Represent the shape and location of geographic objects, such as street centerlines and streams, too narrow to depict as areas. Lines are also used to represent features that have length but no area, such as contour lines and boundaries.
    3. Polygons: A set of many-sided area features that represents the shape and location of homogeneous feature types such as states, counties, parcels, soil types, and land-use zones.
    4. Annotation: Map text including properties for how the text is rendered–annotation can also be feature linked and can contain subclasses.
    5. Dimensions: A special kind of annotation that shows specific lengths or distances, eg. the length of a side of a building
    6. Multipoints: Features that are composed of more than one point. Multipoints are often used to manage arrays of very large point collections, such as lidar point clusters, which can contain literally billions of points. Using a single row for such point geometry is not feasible. Clustering these into multipoint rows enables the geodatabase to handle massive point sets.
    7. Multipatches: A 3D geometry used to represent the outer surface, or shell, of features that occupy a discrete area or volume in three-dimensional space. Multipatches comprise planar 3D rings and triangles that are used in combination to model a three-dimensional shell. Multipatches can be used to represent anything from simple objects, such as spheres and cubes, to complex objects, such as iso-surfaces and buildings.

2 thoughts on “What are Feature Classes?”

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