Scope and Buffer Regions

When selecting data by area, consider the scope of any rules run in your session.

The scope of a rule is the minimum area required to check conformance.

For a rule that checks every point is within 100 units of another point, the rule scope for a circular area centred on the point of interest, with a radius of 100 units.

In some cases, the rule scope is not completely known so a check may produce a false result.

Additional areas outside of the known region must be taken into consideration to obtain correct results.

For example, if the scope is outside the boundary of known data, a false negative is returned when checking for points within 100 units of the root point.

To counteract this, you can set a Buffer.

The Buffer parameter can be used when data is selected using the following methods (see Opening and Selecting Data):

• Single polygon
• Multiple polygons
• Bounding Box
• Webservice polygon

The Buffer is measured in dataset units (typically meters), and the default is 0. Decimal degrees for latitude and longitude can also be used.

In our example, a buffer of 101 could be set to ensure all conformance checks will be valid.

For a region that is defined by a rectangle, the initial rectangular area exists for the scope, while a larger rounded rectangle covers the buffer.

The coordinates in the example below show the initial rectangular and the larger rectangle (buffer region).