You can add an attribute to all objects in a base layer at once using the Attribute Table.
To do so, follow these steps:
- Select the Base layer in the Contents window.
- Click Map Tools | Layer Tools | Open Attribute Table.
- In the Attribute Table, click the Add Field button ().
- Enter a name (e.g. "ZLEVEL").
- Select Numeric for Attribute type and click OK.
- The attribute has been added to all objects in the Base layer, but does not contain any values yet.
- You can populate/view/edit the contents of the column either in the Attribute Table, or you can select an item and click the Info tab in the Properties window to edit or view the new attribute.
Updated November 1, 2021