Working with fields in shapefiles by adding a field in ArcMap

ArcGIS allows you to modify the structure of shapefiles and dBASE tables by adding and deleting fields or attribute columns. The name and data type of an existing field can't be modified; instead, you must add a new field with the appropriate name and data type. A field's name must be no more than 10 characters in length; additional characters will be truncated. After adding fields, you must start an edit session in ArcMap to define their attribute values.

You can also add fields with the Add Field tool.

The field data types supported by ArcGIS are discussed in Geodatabase field data types. The topic How data converts when importing has tables that show how data types for several data sources are mapped to the ArcGIS geodatabase field data types.

Steps:

1. In ArcMap, right-click the shapefile layer in the table of contents and click Open Attribute Table.
2. Click the Options button and click Add Field.
3. Type a field name in the Name text box.
4. Click the Type drop-down arrow and click a type.

   The properties that are appropriate to the new field's data type appear in the Field Properties list.

5. Click in the Field Properties list and type the properties. Properties may include the following:
   • Precision—The number of digits that can be stored in a number field. For example, the number 56.78 has a precision of 4.
   • Scale—The number of digits to the right of the decimal point in a number in a field of type float or double. For example, the number 56.78 has a scale of 2. Scale is only used for float and double field types.
   • Length—The length of a text field specified in characters.
6. Click OK.