Mask DEM with Gazetteer

This is an example of buffering.

From the Edit button on the Table display window of the database.  You must have a gazetteer loaded with the map; one way to do this is to use the Load, Gazetteer menu choice popup menu.

Set the radius for each type of feature by editing the gazetteer symbols file before you attempt this operation.

Pick categories to use for the masking.

Select masking options (buffer size and whether to mask out or in).

DEM has been masked with USGS gazetteer database with just schools selected.

On the left, points outside a 500 m radius have been eliminated, while on the right those within a 500 m radius have been eliminated.

This could model the effects of a school drug free zone, for example.

This creates a bitmap with the database plotted, and compares the color with the desired masking inside or outside the areas).  For best results, in terms of both speed and accuracy, use a 1:1 map view.  If the 1:1 map will be large, you will be asked for the zoom factor to use.

Last revision 10/6/2007