Masking is a way to clarify dense or detailed map content by having the features of one layer mask or block out features of another layer where they overlap. A common use for masking is to mask features around text to ensure the text remains legible.
For example, in an elevation map, contour lines and text may conflict. Leaving the colored elevation polygons intact but masking portions of the contour lines retains the elevation message of the map but makes the contour text more legible.
There are two approaches to masking. Layer masking is where all the features of one layer mask any overlapping features of another layer in the map or scene. Feature level masking is where masking is handled per feature as specified by a relationship class between two layers.
With either type of masking, the geometry of the masking features masks the symbology of the masked features. So, even if the symbolized shape of the masking features differs from the geometry, (for example because a symbol buffer is applied), it is the shape of the feature geometry that does the masking. It is the symbology of the masked features that is impacted. So, a masked feature may appear to have holes, but they are just holes in the visible symbol. The feature geometry is unchanged.
Any feature layer can be masked but only polygon features can be masking features. Layers in the 3D category of a scene cannot be masked, but they can be used as masking layers.
Use layer masking
Layer masking masks the symbolized features of the current layer with the features from one or more polygon masking layers in the map or scene.
- Highlight one or more layers to be masked in the Contents pane.
- Under Feature Layer, on the Appearance tab, in the Drawing group, click Masking .
- In the drop-down menu, check one or more masking layers.
Use feature level masking
You can establish masking on a per feature basis by setting up a many-to-many relationship class between a masked layer and a masking polygon layer. The relationship class is used to link masking polygons with specific masked features.
An easy way to get feature level masking is to use geoprocessing to discover feature conflicts and build the masks for you. Use the Create Overpass or Create Underpass tool to identify conflicts, generate mask polygons and set up relationships automatically. You can edit the resulting masking polygons created by the tool and create new masks if necessary.
Alternatively you can use an existing polygon feature class and create a many-to-many relationship class between it and the masked layer using the Create Relationship Class tool.
- Ensure that a masking polygon feature class is present in the map, along with a many-to-many relationship class relating it to the masked layer. You can turn on the masking polygon features in the Contents pane to see the features, but turn it off when masking is applied to reveal the masking effect.
- Select the layer you want to apply masking to in the Contents pane.
- On the Appearance tab, in the Drawing group, click Symbology to open the Symbology pane.
- Click the Menu button and click Advanced.
- Under the Feature level masking heading, check a relationship class to enable masking. You can activate multiple relationship classes if more than one is available.
The masking polygons mask the features of the current layer.