The geometry service helps applications do geometric calculations such as buffering, simplifying, calculating areas and lengths, and projecting. Additionally, the ArcGIS Web APIs use the geometry service to create and modify feature geometries during web editing. The geometry service provides an alternative to doing these calculations using fine-grained ArcObjects methods or a geoprocessing service.
The geometry service is automatically created for you in the Utilities folder when you create an ArcGIS Server site. It is only visible to publishers and administrators and can be configured through ArcGIS Server Manager. Also, publishers and administrators can see the geometry service and discover its REST URL using the ArcGIS Server Services Directory.
Those who make user connections to the server do not see the geometry service. However, they can benefit from the increased functionality that the geometry service provides through client applications developed with the ArcGIS Web APIs.
Administering the geometry service
By default, the geometry service is not started after you create an ArcGIS Server site. Before you can use the geometry service to do geometric calculations, you must start it. You can also start multiple instances of the geometry service. See Start the geometry service in ArcGIS Server Manager for instructions.
If you want to move the geometry service from the Utilities folder to another folder on the server, you need to delete the service and re-create it. See Re-create the geometry service for instructions.
Developing with the geometry service using the ArcGIS Maps SDK for JavaScript
The ArcGIS Maps SDK for JavaScript contains examples of how to consume the geometry service through code to create or make changes to feature geometries.