Overlay analysis

Overlay analysis is at the heart of geographic insight — it allows you to combine, compare, and extract information from multiple spatial layers.

Crop — “cut features to the boundary”

What it does.

Crop trims features so only parts inside a polygon remain. Example: cut road lines to the city boundary so there are no tails outside the city.

PostGIS Function

Aino trims features using ST_Intersection (to keep only geometry inside a boundary). It also applies ST_MakeValid() to repair broken geometries and ST_CollectionExtract() (or ST_Dump()) to ensure results are proper lines or polygons.

Example

1. Create the dataset with roads that are within the city boundary. Streets have tails outside the boundary area.:

1. Run the prompt:

Crop all roads to the Rendsburg boundary

1. Result: AIno displays only clipped portions of the original features, bounded by the specified area.

Map behavior

Aino shows only road segments inside the city boundary (original tails are removed). Optionally show the original layer for comparison.

Attribute table behavior

Each row is a clipped geometry with fields like road_id, name, length_original, length_cropped, pct_kept. Features with no overlap are not listed.

Intersect — “find overlapping features”

What it does

Intersect returns the exact area where two layers overlap. Useful for identifying areas of impact, risk, or shared coverage — for example, parcels that fall inside flood zones.

PostGIS function

Aino detects overlapping features using ST_Intersection to compute shared geometry, and often uses ST_Intersects in the query filter to speed up the process.

Example

1. Find where farmland and flood zones overlap to assess affected parcels.

1. Run the prompt: Which census tracts are prone to flooding? Highlight them on the map

1. Result: Aino displays only the polygons where both layers overlap and lists the overlap area in the table.

Map behavior

Only the overlapping sections appear, highlighted or shaded for clarity.

Attribute table behavior

Each row represents an overlapping area. Attributes from both layers are shown together.

Combine — “combine 2 datasets into one”

What it does

Merge joins multiple datasets of the same geometry type into one unified layer. Each feature remains separate — boundaries are not dissolved.

PostGIS function

Aino combines datasets using ST_Collect() or ST_Union() depending on the type of merge. It may also add a source_dataset field to track where each feature came from.

Example

1. Create/upload 2 datasets

1. Run the prompt: Combine Parks and Forrests into a new dataset

2. Result: Aino creates one merged layer containing all district polygons from both datasets.

Map behavior

All features from the input layers appear in one map layer. Boundaries remain distinct.

Attribute table behavior

All original rows appear in the table, with a new source_dataset column that records the origin of each feature.

Union — “preserve and integrate all layers”

What it does

Union combines two or more layers so every area from each is included. Overlapping parts are split and attributes from all layers are kept.

PostGIS function

Aino fuses layers using ST_Union to integrate all geometries and preserve overlaps. It may also use ST_SnapToGrid() to clean up edges and ST_MakeValid() to fix geometry issues.

Example

1. Create a land-use dataset by category. Each element is presented as a separate geometry

1. Run the prompt: Union all geomtry into one element in Landuse Dataset

2. Result:

Aino creates a new layer showing all park and lake areas, including the regions where they overlap.

Map behavior

The resulting map shows all unique and overlapping areas as one integrated layer.

Attribute table behavior

Each geometry contains attributes from both sources. Where data doesn’t overlap, empty (null) fields appear.