9.2 Spatial Selections & Location Queries
Key Takeaways
- The Select Layer By Location geoprocessing tool selects vector features based on topological and spatial relationships with features in a secondary selecting layer.
- Core parameters require defining Input Features (the layer being selected from), Selecting Features (the reference layer), and a Spatial Relationship rule.
- Search Distance (buffer selection) enables selecting features within a specified geodesic or planar distance of the selecting features.
- Topological relationships include Intersect, Within a distance of, Completely contain, Are completely within, Touch the boundary of, Share a line segment with, Have their center in, and Overlap.
- Interactive map selection tools (Rectangle, Polygon, Lasso, Circle, Line) allow analysts to manually select features visually directly from the map canvas.
9.2 Spatial Selections & Location Queries
While attribute queries select features based on non-spatial tabular data, spatial queries evaluate topological position and geographic relationships between features across layers. In ArcGIS Pro, spatial selection allows GIS analysts to identify features based on how they overlap, intersect, contain, or neighbor other geographic features—such as identifying all flood risk parcels intersecting a 100-year floodplain polygon, or finding all elementary schools within 500 meters of a major highway.
The Select Layer By Location Geoprocessing Tool
The primary geoprocessing tool for performing location-based selection is Select Layer By Location, located on the Map ribbon under the Selection group or in the Geoprocessing pane.
Primary Input Parameters
- Input Features (Target Layer): The layer containing the features you want to select from. The selection state will be applied to this layer.
- Selecting Features (Source/Reference Layer): The layer used as the spatial template or criteria for making the selection.
- Relationship: The topological or spatial criteria used to evaluate candidate features.
- Search Distance: An optional parameter specifying a buffer distance around the selecting features. If supplied, candidate input features will be selected if they fall within this specified search tolerance distance.
- Selection Type: Controls how the resulting spatial selection interacts with active selections on the input layer (New selection, Add to selection, Remove from selection, Select subset from selection).
Spatial Relationship Types & Topological Rules
ArcGIS Pro supports a comprehensive suite of spatial relationship rules. Selecting the correct spatial relationship is crucial for obtaining mathematically accurate analytical results:
1. Intersect
The default and most common spatial relationship. A feature in the Input layer is selected if any part of its geometry touches, overlaps, crosses, or falls entirely within any feature of the Selecting layer. It is a broad, inclusive spatial search.
2. Within a Distance Of (Buffer Selection)
Selects input features that fall within a specified straight-line (planar or geodesic) distance of any selecting feature. For example, selecting water wells within a 1-kilometer search distance of a point representing a chemical spill site.
3. Completely Contain vs. Contain
- Completely Contain: An input feature is selected only if every vertex and interior point of the selecting feature lies entirely inside the input feature, with no shared boundaries or exterior points.
- Contain: Similar to completely contain, but allows the boundary of the input feature to touch the boundary of the selecting feature.
4. Are Completely Within vs. Within
- Are Completely Within: An input feature is selected only if its entire geometry lies strictly inside the boundary/interior of a selecting feature, without touching the outer boundary of the selecting feature.
- Within: An input feature is selected if its geometry is inside the selecting feature, allowing shared boundaries.
5. Touch the Boundary Of
Selects input features that share a boundary (vertex or line segment) with a selecting feature, but do not share any interior space. For example, selecting adjacent administrative county polygons that share a boundary line with a target state boundary.
6. Share a Line Segment With
Selects features that share a common continuous linear segment. This rule applies to line-on-line or polygon-on-polygon topologies (e.g., identifying road segments that share a common center line segment with municipal boundary lines).
7. Have Their Center In
Selects an input feature if its geometric center (centroid) falls within the boundary of a selecting feature. This is particularly useful when selecting complex polygon features (such as large zip code areas) whose outer boundaries might overlap multiple boundaries, ensuring each input feature is assigned to exactly one selecting polygon based on centroid location.
8. Overlap
Selects input features that intersect a selecting feature of the same geometry type (polygon-on-polygon or line-on-line), where the overlapping region has the same dimension as the inputs, but neither feature completely contains the other.
Interactive Selection Tools on the Map Canvas
In addition to automated geoprocessing queries, ArcGIS Pro provides a suite of interactive screen selection tools on the Map Ribbon (Selection Group). Analysts can draw graphic shapes directly over the map canvas to visually select underlying layer features:
Interactive Selection Shapes
- Rectangle (Default): Drag a rectangular bounding box over the map canvas. Any feature touching or falling inside the box is selected.
- Polygon: Click multiple vertices to define a custom polygon shape around features of interest. Double-click to complete the shape.
- Lasso: Click and hold to draw a freehand sketch path around target features.
- Circle: Click the center point and drag outwards to define a radial selection circle.
- Line: Click to draw a polyline across features; any feature intersected by the drawn line is selected.
Controlling Interactive Selection Behavior
- Selectability by Layer: In the Contents pane, switch to the List By Selection view tab. Here, analysts can check or uncheck individual layers to make them selectable or non-selectable. This prevents accidentally selecting background basemaps, aerial imagery, or reference boundary layers during interactive workflows.
- Selection Tolerance: Configured in ArcGIS Pro Options (Selection tab), defining pixel tolerance for interactive mouse clicks.
Selection Combination & Management Workflows
Spatial selections in ArcGIS Pro can be chained together or combined with attribute selections:
- Chaining Attribute and Spatial Queries: An analyst can run Select Layer By Attribute to select all commercial parcels, then run Select Layer By Location using Select subset from current selection mode to filter those commercial parcels down to only those within a flood zone.
- Switching and Clearing Selections: The Map ribbon provides quick access to Switch (inverting the selected set) and Clear (removing active selections across all visible layers).
- Saving Selections: Active selections can be converted into temporary map layers by right-clicking a layer in Contents and choosing Selection > Make Layer From Selected Features, creating a selection view without exporting data to disk.
A GIS technician needs to find all parcel polygons that have any portion touching or overlapping a designated wildlife corridor polygon layer. Which spatial relationship type in Select Layer By Location is most appropriate?
Which spatial relationship rule selects an input feature ONLY if its entire geometry lies inside a selecting feature polygon without sharing or touching any outer boundary points?
How can an analyst prevent a background parcel boundary layer from being selected while using the interactive Lasso selection tool on the map canvas?