Skip to content

Overlay Analysis

Overlay Analysis

Generally, there are two methods to perform an overlay analysis:

  • Property overlay (polygons)
  • Raster overlay

In Gemini Terrain, we can only run property overlay.

The key elements in a property overlay are input layer, overlay layer, and output layer (result). The overlay function splits the properties in the input layer where they overlap with properties in the overlay layer. New areas with properties from input and overlay layers are stored in the output layer (the original input layer is not changed).

Example

Input data

Overlay

Output

Procedure

  1. Select the method to be used
  2. Add the application layers (input and overlay layers) to be included in the analysis
  3. Check off which properties should be included
  4. Run the analysis

The result (output) from the analysis is placed on the clipboard. This can be pasted into an application layer according to the information in the message field.

Overlay Analysis in Practical Use for Documenting Site Quality

Run overlay analysis with slope maps, aspect maps, and sun/shadow maps.

Overlay with the "union" method (in practice, it doesn't matter what you choose if all layers are clipped against the same boundary contour).

Create an application layer for site quality from a template and then paste the result from the analysis.

The layer has a property called SUITABILITY. The point is to find the combinations of properties that give the following values for suitability:

  1. Poor
  2. Moderate
  3. Good

Suggested Procedure

  1. Remove properties we don't need (e.g., FROM-direction/TO-direction)
  2. Set everything to Good
  3. Sort by slope, select everything steeper than 0.25. Set to Poor
  4. Sort by aspect, select everything that is East. Set to Poor
  5. Sort by shadow, select everything in shadow. Change those that are Good to Moderate

Info

We can take statistics on areas in the Site Quality layer.