The radius (a.k.a. Distance) drop-down allows users to select from a range of pre-set distances within which results should be displayed.

To add a radius drop-down to your locator, click as shown to add the field to the search form:

To control the list of available distances (or radii), update the comma-delimited list of values as shown in the settings for the Radius field.

The units of measurement are controlled by this setting:

The unit of measurement can also be controlled dynamically based on the visitor's country of origin, as described here.

When the radius drop-down is not added to the search form as described above, the system uses the Default distance setting to control the radius value as found under Search Form Settings.