Geometry

Base class for all classes that represent geometric shapes. Geometry is the base class for two-dimensional (x,y) or three-dimensional (x,y,z) geometries. Objects that inherit from the Geometry class may also include a measure (m-value) for each vertex. The Geometry class provides functionality common to all types of geometry. Point, Multipoint, Polyline, Polygon, and Envelope all inherit from Geometry and represent different types of shapes.

Geometry represents real-world objects by defining a shape at a specific geographic location. It is used throughout this API to represent the shapes of features and graphics, layer extents, viewpoints, and GPS locations. It is also used, for example, to define inputs and outputs for spatial analysis and geoprocessing operations and to measure distances and areas.

All types of geometry:

• Have a SpatialReference indicating the coordinate system used by its coordinates

• Can be empty, indicating that they have no specific location or shape

• May have z-values and/or m-values to define elevation and measures respectively

• Can be converted to and from JSON to be persisted or to be exchanged directly with REST services

Immutability Most geometries are created and not changed for their lifetime. Examples include features created to be stored in a geodatabase or read from a non-editable layer, and features returned from tasks such as a spatial query, geocode operation, network trace, or geoprocessing task. Immutable geometries (geometries that cannot be changed) offer some important benefits to your app. They are inherently thread-safe, help prevent inadvertent changes, and allow for certain performance optimizations.

Instead of changing the properties of existing geometries, you can create and update geometries using the various subclasses of GeometryBuilder (for example, PolygonBuilder), which can represent the state of a geometry under construction while allowing modifications, thus enabling editing workflows.

Additionally, GeometryEngine offers a range of topological and spatial transformations that read the content of existing geometries and create new geometries, for example, project, buffer, union, and so on. Relational tests such as intersects and overlaps are also available on GeometryEngine.

Coordinate units The coordinates that define a geometry are only meaningful in the context of the geometry's SpatialReference. The vertices and spatial reference together allow your app to translate a real-world object from its location on the Earth to its location on your map or scene.

In some cases, a geometry's spatial reference may not be set. For example, a Graphic that does not have a spatial reference is drawn using the same spatial reference as the MapView to which it was added. If the coordinates are in a different spatial reference, the graphics may not display in the correct location, or at all.

When using GeometryBuilder to create a Polyline or Polygon from a collection of Point, you don't need to set the spatial reference of every point before you add it to the builder, as it is assigned the spatial reference of the builder itself. In most other cases, such as when using a geometry in geometry operations or when editing a feature table, Geometry.spatialReference must be set.

Spatial reference and projection Changing the coordinates of a geometry to have the same shape and location represented using a different SpatialReference is known as "projection" or sometimes as "reprojection". Because geometries are immutable, they do not have any member methods that project, transform, or otherwise modify their content.