Communicating that only one object can be "default"

Question

A project we're working on has place objects with attributes like name, address, phone number, and URL. Users can view a place and click to call, map, or browse their site.

In our project, one and only one place can be set as the "default" place, meaning that its fields are used as the fallback for all empty fields of non-default places. So if a user clicks to call the Sales department, but they don't have a number listed, it will call the default place (Reception, for example) instead.

A content manager creates the places using a set of web forms, but the problem we're running into is how to label the "default place" field in a way which clearly communicates that this will take the "defaultness" from the old default place.

How do we communicate that there can only be one default place?

Related, we're debating whether it should be a checkbox that can be checked while editing a place ("default" as an attribute) or a button the manager clicks while viewing a place ("make default" as an action).

Do you choose a default place by checkbox or button?

Answer 1

Use a button. Buttons are used for actions to be carries out by the system. In this case, make the item default and un-default the previous default. But be sure to completely communicate how it'll work by adding microcopy.

[make default]
(only one item can be default)

Or when the current item is the default:

[the current item is the default]

Answer 2

When the user makes one place the default, it may also removed default status from a previous place. Checkbox does not make it clear. In this context use a button.

Ulrich's suggestion also works.

Answer 3

The opening paragraph makes this project sound like a city map and you can click on a location on the map and pull up the mentioned details while the example is a department location within a company. The default "place" makes sense for the example but a default for the city map makes no sense.

In situations such as the example I have used the a hierarchy where the "Company" level is the default, then a department would have any variations to the default and in the system I wrote you could have people in the department and they could have their own level, (say private mobile numbers), and inherit from the department and then the company.