5.7. Masking Data for Analysis Layers

When using an analysis layer (for now only created by the Kernel Density Map), often the analysis layer has a significant amount of data falling "outside" of the area of interest. To help remedy this, Cartographica can constrain the bounds of the analysis layer to the area of a polygon layer.

Below are examples of an analysis layer, the mask to be applied, and the resultant masked analysis layer. In this case, we use a Kernel Density Map and have a satellite map in the background as illustration.

Analysis Layer without Mask

Figure 5.6. Analysis Layer without Mask

Analysis Layer Mask

Figure 5.7. Analysis Layer Mask

Analysis Layer with Mask

Figure 5.8. Analysis Layer with Mask

Masking an analysis layer

In order to mask an analysis layer, you need to have a polygon layer that specifies the area you want included in the analysis. You can either use an existing polygon layer, or create one manually or using tools such as Cartographica's Tools  >  Make Convex Hull

  1. Select the analysis layer in the layer stack by clicking on it

  2. Select the polygon layer in the layer stack by holding the option key while clicking on it

  3. Choose Layer  >  Set Mask Layer

    After a few seconds, the analysis layer will be masked by the polygon layer you selected.


    The mask layer will work even if the mask layer is hidden, so you can add a layer to act as the mask, assign it to the analysis layer, and then hide the mask layer without losing the mask effect, but without having whatever data is in that layer displayed.

Removing an analysis layer mask

  1. Select the analysis layer in the layer stack by clicking on it

  2. Choose Layer  >  Clear Mask Layer