Overlay Analysis

Overlay analysis is a fundamental GISGISGeographic Information Systems (GIS) enable users to analyze and visualize spatial data to uncover patterns, relation... technique that combines multiple geospatial layers to produce new datasets reflecting the spatial interaction between input features. By superimposing layers and computing their geometric intersections, unions, or differences, overlay analysis reveals relationships and patterns that are not visible in any single dataset. This capability makes it one of the most powerful and widely used tools in spatial analysis.

Overlay analysis encompasses several distinct operations, each serving different analytical purposes. Intersection extracts only the areas where input layers overlap, retaining attributes from both. Union combines all features from input layers, preserving geometry and attributes from every region whether overlapping or not. Difference (erase) removes the area of one layer that falls within another, useful for identifying exclusion zones. Symmetric difference retains areas that are in either layer but not in both. Identity preserves the full geometry of one input while splitting it at the boundaries of another, appending attributes from the overlapping areas.

Overlay analysis is central to multi-criteria decision making and suitability modeling. Site selectionSite SelectionSite selection is the analytical process of evaluating and choosing optimal physical locations for new stores, facili... for new facilities involves overlaying layers for zoningZoningZoning is a land use planning tool that divides geographic areas into zones with specific permitted uses, building st..., demographics, transportation access, and environmental constraints to identify optimal locations. Environmental impact assessment overlays proposed development footprints with habitat maps, wetland boundaries, and protected areas to evaluate ecological consequences. Land-use planning combines current land cover, ownership parcels, infrastructure networks, and regulatory zones to develop comprehensive plans. Agricultural management overlays soil type, slope, drainage, and climate layers to determine crop suitability. Emergency management combines hazard maps with population density and critical infrastructure layers to assess vulnerability.

Overlay analysis enables the synthesis of diverse spatial information into unified analytical outputs. It supports both vector and raster dataRaster DataRaster data represents geographic information as a grid of cells or pixels, where each cell holds a value representin... models, providing flexibility across different data types. The technique is highly scalable, from simple two-layer intersections to complex multi-layer suitability models with weighted criteria. Results are spatially explicit, producing new map layers that can be further analyzed or visualized.

Overlay operations on vector dataVector DataVector data represents geographic features as discrete points, lines, and polygons with associated attribute informat... can produce topological artifacts such as sliver polygons at boundaries where input layers do not align precisely. Computational performance degrades with increasing geometric complexity and dataset size. Combining layers in different coordinate systemsCoordinate SystemsCoordinate systems standardize the description of geographic locations using latitude, longitude, and other spatial d... requires reprojection, which can introduce spatial errors. The interpretation of overlay results depends heavily on the quality and currency of input data.

Raster-based overlay using weighted suitability modeling is increasingly integrated with machine learning for predictive spatial analysis. Cloud-based GISGISGeographic Information Systems (GIS) enable users to analyze and visualize spatial data to uncover patterns, relation... platforms enable collaborative multi-layer overlay analysis with shared datasets. Real-time overlay of dynamic data streams, such as combining live traffic with infrastructure layers, is enabling new operational applications.