Working with pre-9.2 spatial references
Prior to ArcGIS 9.2, spatial references were low precision. Each integer coordinate was allotted 31 bits rather than the 53 bits provided by high-resolution spatial references created and maintained with versions 9.2 and higher. With low precision, you have to specify a domain extent as well as a resolution value. A large domain extent is only possible with low resolution values. Consequently, values reflecting a high resolution demanded undersized domains, which were often too small for many projected coordinate systems such as universal transverse Mercator (UTM) or state plane.
With a high-precision spatial reference, the resolution and coordinate system define an extent for your dataset, cutting out the need for a user-defined domain extent. The default resolution of 0.0001 meters is precise enough for most data and does not restrict your extent as a low-precision spatial reference would. Therefore, there is no need to strike a balance between domain extent and resolution with a high-precision spatial reference since it offers both in unison.
To take advantage of these benefits, converting data to high precision is recommended in most cases. If you have to deliver data to clients who have not upgraded or you are satisfied with your existing situation, you do not need to convert your data to high precision. The data will continue to work in ArcGIS as it always has, and you can continue to create new datasets with low-precision spatial references.
Converting a low-precision spatial reference to high precision
Converting personal geodatabase data to high precision takes two steps: upgrading your geodatabase and upgrading your spatial reference.
To upgrade your personal geodatabase, open the geodatabase properties in the Catalog tree. On the General tab, click the Upgrade geodatabase button. This updates the geodatabase schema. This does not convert any existing spatial references to high precision. Because of this, you can continue to create new low-precision feature classes within any existing low-precision feature dataset if you want.
To convert existing spatial references to high precision, use the Upgrade Spatial Reference geoprocessing tool in the Data Management Tools toolbox under Database.
For more information on converting to high precision via this and other methods, see Migrating to high precision.
Creating low-precision spatial references
In ArcGIS 9.2 and higher, you can continue to create low-precision datasets by using a pre-9.2 geodatabase that has not been through the upgrade process. If you create a new feature class or feature dataset with this geodatabase or import data into it, the new data will have a low-precision spatial reference. If you have upgraded a pre-9.2 geodatabase, existing feature datasets are still low precision until you upgrade the spatial references. Because of this, you can create a new low-precision feature class within an existing low-precision feature dataset. You cannot create low-precision stand-alone feature classes or feature datasets within any new geodatabase you create with ArcGIS version 9.2 or higher, or within any geodatabase you have upgraded to version 9.2 or higher.
If you're uncertain about the version of a geodatabase, right-click the geodatabase in the Catalog tree and click Properties. The Upgrade Status section shows the version.
When creating a low-precision spatial reference, you may need to carefully balance the trade-off between domain extent and the resolution or precision values. For detailed information on how to specify a low-precision spatial reference for your data, see Choosing the resolution and domain of a low-precision spatial reference.