Overlay analysis involves processing or analyzing spatial data to extract new spatial geometry information required by users. For example, to understand soil distribution within a specific administrative region, overlay analysis can be performed using a national land use map and administrative division map datasets to obtain desired results. Additionally, overlay analysis enables processing of various data attributes.
Overlay analysis is widely applied in resource management, urban development assessment, land management, agriculture, forestry, animal husbandry, and statistical fields.
Spatial overlay analysis involves logical operations including intersection, union, difference, and XOR. For discussion purposes, Euclidean space layers A, B, and C are defined as binary images. The table below illustrates properties and laws of layer Boolean logic operations.
| Logical Operation | Definition | Properties | Explanation |
| Contain | If x∈A implies x∈B, then A is called a sub-image of B or B contains A, denoted as A⊆B. | (1) A⊆A
(2) A⊆B, B⊆C ⇒ A⊆C (3) A⊆B, B⊆A ⇒ A=B |
If A⊆B and A≠B, A is called a proper sub-image of B, denoted as A⊂B. Ω represents a complete image, φ represents an empty image. |
| Intersection | The intersection of A and B is defined as A∩B = {x|x∈A and x∈B} | (1) A∩A = A
(2) A∩φ = φ (3) (A∩B)∩C = A∩(B∩C) |
If A∩B = φ, A and B are considered disjoint. |
| Union (OR) | The union of A and B is defined as A∪B = {x|x∈A or x∈B} | (1) A∪A = A
(2) A∪φ = A (3) (A∪B)∪C = A∪(B∪C) |
|
| Difference | The difference between A and B is defined as A-B = {x|x∈A and x B} |
(1)A-φ = A
(2) A-A = φ (3) (A-B)-C = A-(B∪C) |
|
| XOR | The XOR of A and B is defined as: A⊕B = {x|x∈A or x∈B, and xA∩B} |
The following diagram illustrates Boolean logic operations: containment, intersection, union, difference, and XOR.
Feature Description
Region datasets used in overlay analysis must not contain overlapping polygon features. Datasets with overlapping features are invalid and may produce incorrect results. It is recommended to perform topology validation before conducting overlay analysis.
Overlapping regions are shown in the following diagram:
Notes:- In overlay analysis, the input dataset (referred to as the first dataset in SuperMap GIS) can be point, line, or polygon type. The overlay dataset (second dataset) must be a region dataset.
- Ensure the region dataset contains no overlapping areas to avoid errors in analysis results.
- All datasets involved in overlay analysis must share the same geographic reference system, including input data and result data.
- For large datasets, create spatial indexes for result datasets to improve display performance.
Related Topics
Introduction to Overlay Analysis Tools