Fundamentals of ObjectID fields

The ObjectID field is maintained by ArcGIS and guarantees a unique ID for each row in a table. When you look at a table or a layer's attribute table, you will usually see the ObjectID field listed under the aliases of OID or ObjectID. Key functions, such as scrolling and displaying selection sets, depend on the presence of this field.

Most data sources supported by ArcCatalog and ArcMap provide an ObjectID field with their tabular data. In these cases, the ObjectID field is accessed directly and used by the Table window in ArcMap and table preview in ArcCatalog. The following data sources, however, do not contain an ObjectID field with their tabular data:

ObjectID fields are sequential and start with the number 1 for geodatabase data. For shapefiles and dBASE tables, the OID or FID column begins at 0.

If you are unsure what type of table you're working with and whether it has an ObjectID field, you can quickly find out. In ArcMap, on the top of the table of contents window click the List By Source button List By Source, right-click the table in the table of contents, then click Properties. Click the Source tab on the Table Properties dialog box and look for either a Yes or No for the Has Object-ID Field entry. In ArcMap or ArcCatalog, you can open the table's Properties dialog box and click the Fields tab. If there is no field listed with an ObjectID data type, the data does not have an ObjectID field.

If your table lacks an ObjectID field, you won't be able to perform the following operations:

There are several ways of obtaining an ObjectID field for your data:


ArcGIS and the geodatabase cannot consume 64-bit integers. The maximum possible ObjectID value is 2,147,483,648.

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