Polygonal Restriction
On the Polygonal Restriction tab of the Trend Surface form, you can restrict the output data by applying a polygonal (String or Outline) restriction.
String File
Select a file Type and then double-click (F3) to select the input File that contains the polygons you want to use to restrict the data. Optionally, apply a Filter to limit the records to a particular subset of data.
X, Y fields
Double-click (F3) to specify the names of the fields in which Easting and Northing coordinates are stored.
Join field
In forms that require polylines as an input, the values in this field define whether the data points in the input file should be joined by a line. If successive records have the same value in this field, a line will join the points. If two-factor topology is required, the values in a String field may also be used to segment the lines.
String field
In most forms, the String field is an optional generic attribute used to store a secondary input such as a code. Traditionally, this field has also been used with the Join field to define whether data points should be joined by a line, or strung, hence the name.
Outline File
Select this option and click the More button to select an Outline file containing the outlines you want to use to restrict the data.