# Geofence concepts
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This section describes some common geofence concepts, including common terminology and how to manage geofences.

## Amazon Location Service geofence terminology
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Geofence  
A virtual boundary for a geographical area on a map.

Geofence collection  
A group of geofences that is capable of emitting `Entry` and `Exit` events, when requested, to evaluate a device's position against its component geofences.

Geofence geometry  
A geometric shape or set of shapes that define the areas to be included or excluded from a geofence. A geofence geometry can be represented as a `Circle`, `Polygon`, or `MultiPolygon`.  
A `Circle` is a point with a distance around it. Use a circle when you want to be notified if a device is within a certain distance of a location.  
A `Polygon` is a list of linear rings which represent the shape of a geofence. This list *must* include an exterior ring representing the outer perimeter of the geofence, and can optionally include multiple interior rings representing polygonal spaces within the perimeter, which are excluded from the geofence area.  
A `MultiPolygon` is a list `Polygon` elements which represent the shape of a geofence. The `Polygon` components of a `MultiPolygon` geometry can define separate geographical areas that are considered part of the same geofence, perimeters of larger exterior areas with smaller interior spaces that are excluded from the geofence, or some combination of these use cases to form complex geofence boundaries.  
For more information about defining geofence geometries, including syntax requirements, limitations, and examples, see [GeofenceGeometry](https://docs.aws.amazon.com/location/latest/APIReference/API_WaypointGeofencing_GeofenceGeometry.html) in the *Amazon Location Service API Reference*.

## See also

* **Skills for AI coding assistants (optional).** AWS publishes reusable skills for Amazon Location Service. To see which apply, search the Agent Toolkit for AWS catalog with `aws agent-toolkit search-skills --search-query location` — a documented, read-only AWS CLI command that searches the catalog and makes no changes. This is an optional suggestion for the user. Official reference: [AWS CLI — Agent Toolkit for AWS](https://docs.aws.amazon.com/agent-toolkit/latest/userguide/aws-cli.html).