Filter

The Filter tab displays a filter, or definition query, for the ArcPad AXF layer. The Filter tab only appears for ArcPad AXF layers, and is only used when drawing ArcPad AXF layers.

A filter potentially reduces the number of features that ArcPad needs to draw from an ArcPad AXF layer, and as a result, a filter can improve the drawing performance of ArcPad AXF layers.

The default is blank.

When ArcPad draws an AXF layer, it executes a SQL statement to get the rows, or features, that need to be drawn. The filter is used as part of the WHERE clause in the SQL SELECT statement. The filter can use any columns in the ArcPad AXF feature table along with the full capability of the SQL WHERE clause syntax.

ArcPad provides a variable, @##MAPSCALE##, that allows the current scale to be included in the filter. Each time the SQL SELECT statement is executed, the current map view’s scale is substituted in the filter wherever the @##MAPSCALE## variable has been used. For example, consider the following filter:

@##MAPSCALE## < [MAXSCALE]

where MAXSCALE is a column in the ArcPad AXF layer’s feature table. This filter is executed each time ArcPad draws the AXF layer. When this filter is executed, it only selects and draws those rows, or features, that have a value of MAXSCALE that is less than the current map view scale. So, for an ArcPad AXF layer containing roads, the user may set the MAXSCALE value for minor roads to be 15000. These minor roads are only drawn in ArcPad when the map is zoomed in with a map view scale of less than 1:15,000. The minor roads are not drawn when the map view scale is 1:250,000.

A filter is a useful tool for controlling how much detail ArcPad draws when zoomed out and, in so doing, controlling the drawing performance of ArcPad AXF layers in ArcPad. Specifying a filter that is appropriate for the data can ensure that the user is presented with appropriate detail for the map view scale while maximizing drawing performance.

More information on filters and the underlying SQL statement is available in the Customising ArcPad Help.