Create Enumeration Areas

The Create Enumeration Areas tool automates the spatial aggregation and delineation (splitting) of census Enumeration Areas (EAs) based on building household load, spatial contiguity, administrative barangay boundaries, and optional linear feature alignment (roads and rivers).

Access

• Processing Toolbox: GMD Pipeline → 1Map → Create Enumeration Areas
• Algorithm ID: gmd_pipeline:createea
• Menu: Gemma → EA Delineation → Create Enumeration Areas
• Toolbar: Gemma Toolbar → Create Enumeration Areas icon

When to Use

Use this tool when:

• Preparing enumeration area boundaries for national census and demographic field operations.
• Re-balancing EA boundaries to ensure every field enumerator workload falls within a target household range (default 100 to 300 households).
• Delineating overpopulated EAs (>300 households) using building point spatial clustering and road/river network centrelines.
• Merging underpopulated EAs (<100 households) with adjacent contiguous neighbors within the same barangay boundary.

User Interface Features

The dedicated EA Launcher dialog provides an interactive workflow prior to executing the algorithm:

• Auto-Detect Layers: Automatically scans open layers in the QGIS project and selects matching inputs based on standard layer naming conventions (_bgy, _ea, _bldgpts, road, river).
• Fill Missing Household Counts: Includes a built-in pre-processing utility to compute missing household counts (hhcount) directly from building points within each EA polygon before running the algorithm.
• KPI Cards & Live Candidate Preview: Renders dynamic statistics and color-coded candidate tables for Delineation (>300 HH) and Merging (<100 HH) candidates before execution.

Parameters

Inputs

Parameter	Type	Description
Barangay Layer	Vector (Polygon)	Administrative barangay boundaries. Must contain a geocode field representing administrative boundary codes. Required.
Building Point Layer	Vector (Point)	Structure/building point data with an hhcount field representing households per building. Required.
Previous EA Layer	Vector (Polygon)	Starting EA boundaries from the previous census round. Must contain geocode or ean fields. Attributes are inherited by outputs. Required.
Road Layer	Vector (Line)	Road network lines used to snap split boundaries to road centrelines. Optional.
River Layer	Vector (Line)	River and waterway centrelines used for split line snapping. Optional.
Gap Layer	Vector (Polygon)	Polygon layer representing unmapped boundary gaps, extracted into Special EAs. Optional.
Overlap Layer	Vector (Polygon)	Polygon layer representing boundary overlaps, extracted into Special EAs. Optional.
Minimum Household Count per EA	Integer	Minimum target household threshold per EA (default: 100). EAs below this limit are merged.
Maximum Household Count per EA	Integer	Maximum target household threshold per EA (default: 300). EAs above this limit are split.
Optimize for Compactness	Boolean	Prefers spatially compact EA shapes over purely household-balanced splits (default: True).
Sliver Polygon Area Threshold	Enumeration	Controls area threshold for identifying and dissolving remnant sliver polygons into neighboring EAs.
Snapping Tolerance (metres)	Double	Maximum search distance for snapping proposed split lines to road or river centrelines (default: 15.0 m).
Target CRS	CRS	Output Coordinate Reference System (default: EPSG:4326).
Preview Candidates Only	Boolean	When enabled, generates candidate preview layers and exits without altering EA geometries.

Outputs

Output	Type	Description
Output EA Layer	Vector (Polygon)	Consolidated output layer containing all final updated EA polygons (<geocode>_ea2026).
Delineated EAs Layer	Vector (Polygon)	Optional output containing all sub-polygons generated from delineation (<geocode>_delineated_ea2026).
Merged EAs Layer	Vector (Polygon)	Optional output containing only EAs generated from merging underpopulated EAs (<geocode>_merged_ea2026).
Special EAs Layer	Vector (Polygon)	Optional output containing Special EAs generated from Gap and Overlap layers (<geocode>_special_ea).
Candidate for Delineation Layer	Vector (Polygon)	Layer containing EAs identified as candidates for delineation (>300 HH).
Candidate for Merging Layer	Vector (Polygon)	Layer containing EAs identified as candidates for merging (<100 HH).
Extracted Building Points Layer	Vector (Point)	Point layer containing building points tagged with assigned EA identifiers.

How It Works

1. Initialization and Coordinate Transformation:

   • Validates input parameter combinations and transforms all vector layers to the Target CRS (default EPSG:4326).

2. Building Point Spatial Join and Household Aggregation:

   • Performs a spatial join between building points and previous EA boundaries.
   • Calculates total building load (bldg_count) and sums households (hhcount) per EA.

3. Spatial Indexing of Linear and Special Layers:

   • Builds spatial R-tree indexes for road networks, river centrelines, and gap/overlap polygons for fast spatial queries.

4. EA Classification:

   • Categorizes starting EAs into Pass-through EAs (100 to 300 HH), Delineation Candidates (>300 HH or gap/overlap), and Merge Candidates (<100 HH).

5. Single-Pass EA Delineation (Splitting):

   • Overpopulated EAs are split using weighted K-Means clustering on internal building points in a single deterministic pass.
   • Generated cut lines are buffered and snapped to the nearest road or river centrelines within the specified snapping tolerance.

6. Iterative EA Merging:

   • Underpopulated EAs undergo up to 5 iterative passes of spatial adjacency merging.
   • Merging is strictly restricted to 2 contiguous EAs (touches() or intersects()) within the same parent barangay, ensuring combined households do not exceed the maximum threshold (300 HH).

7. Compliance Sweep and Sliver Dissolve:

   • Identifies remnant sliver polygons smaller than SLIVER_THRESHOLD and dissolves them into the largest adjacent neighbor.
   • Applies feature guards to eliminate any empty geometries or unpopulated key identifiers.

8. Output Sink Writing and Attribute Inheritance:

   • Writes final polygons to output sinks while preserving original attribute fields from the previous EA layer.
   • Appends metadata tracking fields including hhcount, bldg_count, split_by (road, river, kmeans), new_ea, and correspondence_ea_geocode.

Supported Geometry Types

• Polygon and MultiPolygon (Barangay, EA, Gap, Overlap layers)
• Point and MultiPoint (Building Point layer)
• LineString and MultiLineString (Road and River layers)

TIP

For best results, verify that building point layer household attributes (hhcount) are populated before running delineation. You can use the built-in Fill missing hhcount button in the EA Launcher dialog to automatically update missing values from building points within each EA.