4. The method of claim 1 , comprising removing a user of the second user device from the social group upon determining that the second user device has left the location.
1. A method comprising: receiving, from a first user device, activity information on an activity performed by a user of the first user device; receiving, from the first user device, a location where the first user device has stayed for at least a threshold amount of time; automatically determining, based on the activity information, a type of the activity; creating a social group based on the location and the type of the activity, including determining a theme of the social group based on the type of the activity; determining that a first condition that a second user device is located at the location or will visit the location is satisfied; determining that a second condition that the second user device seeks information related to the location or related to the theme of the social group is satisfied; and in response to determining that the first and second conditions are satisfied, providing a recommendation to join the social group to the second user device, wherein the method is performed by one or more computers.