Map transparency is a method used to highlight trends in your thematic data and make patterns more comprehensible by varying the level of opacity in map features.

There are several reasons you may want to apply some transparency to a map:

• Some areas of the map are dense with point features. By applying some transparency to the features it is possible to see where they overlap.
• Outlines on polygons might be distracting and pull your audience's attention away from the main thrust of your map. By adjusting the opacity of your area boundaries you can focus more attention to the map topic.
• You want features that have a high value in a thematic map to stand out more than those with a low value. By making features with low values more transparent they will fade more into the background.