You can add fields to your table using ArcCatalog or ArcMap. In ArcCatalog, you need to open the layer or table's Properties dialog box and add the field to the list on the Fields tab. In ArcMap, you can add a field through the attribute table of a layer or through the Catalog window by accessing the same Properties dialog box and Fields tab. Inside either application you can also use the Add Field geoprocessing tool.
You can add or remove fields as long as the following conditions are met:
- You have write access to the data.
- You're not currently editing the data in ArcMap.
- No other users or applications are accessing the data including other ArcMap or ArcCatalog sessions.
- Right-click the table or layer in the table of contents and choose Open Attribute Table.
- Click the Table Options button in the table window.
You can make calculations without being in an editing session; however, in that case, there is no way to undo the results.
- Click Add Field.
- Type the name of the field.
- Click the Type arrow and click the field type.
- Set any other field properties as necessary.
- Click OK.