Feature class geometry

Recall that when you create a new feature class, you must specify the type of geometry that it will store: point (or multipoint), line, or polygon. The feature class geometry determines the types of features that you can create and how they are stored in the geodatabase.

A point feature is the simplest—it is stored as a single pair of x,y coordinates. Line and polygon features are composed of segments. If a segment is a straight line, it is stored as two pairs of x,y coordinates which define the endpoints. If a segment is a curve, it is stored as the coordinates of the endpoints with a formula that defines the curve connecting them.

In a geodatabase, features are stored as one or more coordinate pairs. True curves are stored as a mathematical formula connecting two coordinate pairs

Z (elevation) and m (measure) coordinates can also be stored for each point and for each vertex in a line or polygon feature.

Line and polygon features can be created as single or multipart features. Multipart features are composed of multiple shapes grouped into a single feature which has only one record in the feature class table. In a multipart line feature, the individual parts are called paths. In a multipart polygon feature, they are called rings. Both paths and rings are composed of segments.

For example, as shown below, the seven larger islands of Hawaii can be stored as a single feature. Multipart polygons are also used to represent areas that are completely contained within another area, such as an island in a lake.

Top: The Neches River is divided by three reservoirs which split the river into four paths. Bottom: The state of Hawaii is composed of seven large islands (plus many smaller islands, not shown). Each of these multipart features is represented as a single record in the feature class table.

Both line and polygon feature classes automatically support multipart features, but point feature classes do not. If you want to store multipoint features, you must create a multipoint feature class.