Overlay
Overview
Overlay is a GIS operation that involves combining multiple layers of spatial data to analyze relationships and interactions between different features. Overlay operations are fundamental to spatial analysis, enabling users to answer questions about how different geographic phenomena relate to each other.
Key Concepts
Union combines all features from input layers, preserving all areas. Intersect returns only areas common to all input layers. Erase/Difference removes areas of one layer that overlap with another. Identity preserves input features while adding attributes from overlay layer. Clip cuts features to the boundary of a clip layer. Symmetric difference returns areas in either layer but not both.
Overlay Types
| Operation | Result |
|---|---|
| Union | A + B + (A ∩ B) |
| Intersect | A ∩ B |
| Difference | A - B |
| Symmetric Difference | (A ∪ B) - (A ∩ B) |
Appendix
Created: 2025-12-13 | Modified: 2025-12-13