Changing the precision

If you decide to modify the default values for the spatial domain when creating a feature class or feature dataset, you will find that changes to the precision value result in changes to the spatial extent values. Increasing the precision value decreases the spatial extent, while decreasing the precision value increases the spatial extent.

When you change the precision value, the Max X and Max Y values automatically update to reflect the change.

When you change the precision, the spatial extent changes as well. In this example, when the precision is decreased, the Max X and Max Y values update to increase the allowed spatial extent.

You should choose a precision value that will support the accuracy of your data. If you're setting the precision for a feature dataset that will contain feature classes of varying accuracy, you should use a precision value that will support the highest level of accuracy.

Precision considerations

When choosing a precision value for storing your data, consider the following general guidelines:

· Choose the smallest precision that allows for updates to your data and anticipates future growth, and that supports the highest level of accuracy required for the data.

· If you choose a precision that is too small, the resolution of your data will be decreased and the shape of features may become distorted. If you choose too large a precision, however, your data may imply a higher level of accuracy than it possesses.

· The higher the precision value, the larger the storage requirements for your data will be. High precision values may also result in slower processing speed. This should only be a consideration if you are working with very large datasets.

· An inappropriate precision can affect the cluster tolerance for a topology. As the precision increases, the possible maximum cluster tolerance decreases. Using a precision value that is too high for your data may make the maximum cluster tolerance so small that it becomes difficult to fix topology errors using the ArcMap edit tools. You'll learn about topology and cluster tolerance in the next lab.

You can calculate the precision value you need using the formula below:

For example, if you want to store data at 10-centimeter resolution (in other words, 1 geodatabase storage unit = 10 cm) and your map units are meters (convert meters to centimeters: 1 meter = 100 cm), your formula will use the following values: