PSA - LGU Boundary Comparison

The PSA - LGU Boundary Comparison tool provides an automated auditing and spatial discrepancy evaluation workflow that cross-examines official Philippine Statistics Authority (PSA) reference boundaries against LGU-submitted boundary polygons and geotagged building point datasets. It pairs 8-digit PSGC geocode polygon matching with spatial containment indexing to identify boundary discrepancies and detect mis-allocated building points.

Access

• Processing Toolbox: GMD Pipeline → 1Map → PSA - LGU Boundary Comparison
• Algorithm ID: gmd_pipeline:psalgu_boundary_comparison
• Review Panel Menu: Gemma → Updating of Boundaries → PSA - LGU Comparison Review

The comparison algorithm executes as a standard processing tool and generates styled output layers. Once processing completes in QGIS Desktop, the PSA - LGU Comparison Review dock panel opens automatically to facilitate synchronized side-by-side inspection.

When to Use

Use this tool when:

• Auditing local government boundary submissions against official PSA reference boundaries for municipal harmonization.
• Validating whether geotagged building points physically reside inside the barangay declared in their administrative geocode attributes.
• Telling apart building points that fall outside the LGU-submitted boundary from those that fall outside the official PSA boundary.
• Inspecting matched barangay pairs sequentially with automated zoom framing and dynamic building point filtering.
• Isolating unmatched barangays (declared by either the LGU or PSA but missing in the counterpart dataset) for field review.

Parameters

Inputs

Parameter	Type	Description
PSA Boundary Layer	Vector Layer (Polygon)	Official PSA administrative boundary polygon layer. Auto-selects loaded layers containing _psa or psa in their name.
Geocode Field (PSA)	Table Field	Geocode attribute field on the PSA layer. If omitted, auto-detects a field literally named Geocode.
LGU-Submitted Boundary Layer	Vector Layer (Polygon)	LGU boundary polygon layer to audit. Auto-selects loaded layers containing _lgu or lgu in their name.
Geocode Field (LGU)	Table Field	Geocode attribute field on the LGU layer. If omitted, auto-detects a field literally named Geocode.
Building Point Layer	Vector Layer (Point)	Geotagged building point layer to evaluate against barangay boundaries. Auto-selects layers matching bldgpts, bldg_point, etc.
Geocode Field (Building Point)	Table Field	Geocode attribute field on the building point layer specifying its administrative barangay assignment.

Outputs

Output	Geometry Type	Symbology & Role
<code>_PSA_Matched	Polygon	Blue outline (#1E88E5), labeled with the PSA barangay name. Contains PSA polygons matched to LGU counterparts.
<code>_LGU_Matched	Polygon	Yellow outline (#FBC02D), labeled with the LGU barangay name. Contains LGU polygons matched to PSA counterparts.
<code>_PSA_Unmatched	Polygon	Gray outline. Contains PSA barangays with no corresponding LGU geocode match.
<code>_LGU_Unmatched	Polygon	Gray outline. Contains LGU barangays with no corresponding PSA geocode match.
building points inside lgu boundary	Point	Green circles (#43A047). Building points that physically fall inside the LGU polygon matching their declared barangay geocode.
building points outside lgu boundary	Point	Red circles (#E31A1C). Building points positioned outside the LGU polygon of their declared barangay.
building points outside psa boundary	Point	Purple squares (#9C27B0), drawn slightly larger so a point outside both boundaries still shows both markers. Building points positioned outside the PSA polygon of their declared barangay.

(Note: <code> represents the municipal prefix extracted from the input layer names, e.g. 000102).

All three building point layers are always created, even when empty. An empty Outside layer means no building point fell outside that boundary, not that the check was skipped.

Reading the Outside Layers

Both Outside layers share the same attribute columns, each evaluated against its own boundary source:

Column	Description
geocode_first8	The first 8 characters of the building point's own geocode (the barangay it claims to belong to).
in_geocode	The barangay the point actually sits inside, taken from the same boundary source as the layer (LGU for the LGU layer, PSA for the PSA layer). Empty when the point falls outside every barangay of that boundary.
match_id	Matched-pair ID of the barangay named by the point's own geocode.
in_match_id	Matched-pair ID of the barangay the point physically sits inside.

Comparing the two layers shows where the discrepancy lies:

Point appears in	Interpretation
Outside LGU only	The point is inside the official PSA barangay but outside the LGU-submitted polygon, which suggests the LGU boundary needs review.
Outside PSA only	The point is inside the LGU-submitted polygon but outside the official PSA barangay, which suggests the LGU boundary extends beyond the PSA reference.
Both layers	The point is outside the declared barangay in both sources, which usually indicates a mis-coded geocode (check in_geocode) or a point captured outside the municipality.

On the map, a point in both layers shows a red circle drawn on top of a larger purple square.

How It Works

1. Geocode Prefix Matching:

   • Compares the first 8 characters (first8) of the geocode field (Region + Province + City/Mun + Barangay) between PSA and LGU polygon layers.
   • Bypasses name orthography and trailing digit differences, preventing mismatches caused by minor spelling discrepancies.
   • Preserves multipart geometries, ensuring that multi-island barangays remain unified under a single matching key.

2. Spatial Indexing & Containment Engine:

   • Constructs a spatial bounding box index (QgsSpatialIndex) over the LGU boundary polygons, and a second one over the PSA boundary polygons.
   • Evaluates each building point against the specific LGU polygon, and separately the specific PSA polygon, matching its own 8-character geocode.
   • Points falling inside or intersecting the shared polygon boundary are categorized as Inside; points falling outside go to that boundary's own Outside layer (LGU or PSA). A point outside both appears in both.
   • Building points are reprojected to each boundary layer's CRS before testing when the CRSs differ; output geometries stay in the building layer's original CRS.
   • Points whose geocode names a barangay from a different city or municipality entirely, and that do not physically fall inside the boundary being checked, are excluded from that Outside layer as unrelated to the comparison.

3. Field Collision Prevention:

   • If an input layer already contains an attribute named geocode, QGIS appends duplicate columns as geocode_2.
   • To guarantee that the review panel reads the true barangay geocode, the algorithm stamps the custom layer property psalgu_geocode_field with the exact generated column name.
   • Assigns match_id to matched polygons and both match_id and in_match_id to outside building points, allowing points to be scoped per barangay during review.

4. Automated Post-Processing:

   • Organizes all generated output layers into a dedicated Layer Tree group named <code> PSA - LGU Comparison.
   • Automatically unchecks the visibility of the raw input layers to keep the canvas focused on comparison results.
   • Adds a Google Satellite XYZ basemap below the layers if the HCMGIS plugin is installed.
   • Activates the comparison review dock panel on the QGIS main thread via post-processing interfaces.

Comparison Review Panel

The PSA - LGU Comparison Review dock panel (GemmaPsaLguComparisonPanel) docks beneath the QGIS Layers panel:

1. Barangay Navigation:

   • Select any matched barangay from the dropdown list or navigate sequentially using the Previous and Next buttons.
   • The dropdown displays the clean barangay name and 8-digit geocode.

2. Synchronized Canvas Zoom:

   • The map canvas automatically centers and zooms to the combined bounding box of both the PSA and LGU polygons for the selected barangay.
   • A 15% framing margin (ZOOM_PADDING_RATIO = 0.15) is applied so boundaries are not flush against canvas edges.

3. Dynamic Point Scoping:

   • When stepping through barangays, subset filter strings are dynamically updated on all building point layers:
     • Inside points are filtered by match_id.
     • Outside points are filtered by either match_id (declared barangay) or in_match_id (the physical barangay the point sits inside).
   • This ensures the reviewer only sees building points relevant to the currently inspected barangay.

Supported Geometry Types

• Polygon and MultiPolygon (PSA and LGU boundary layers)
• Point and MultiPoint (Building point layer)

Geocode Text Formatting

Ensure that geocode attribute fields in shapefiles and GeoPackages are formatted as String/Text rather than Numeric/Integer. Numeric formats drop leading zeros (e.g. converting 01030200 to 1030200), causing 8-digit prefix matching to fail.

Headless Execution

The processing algorithm (gmd_pipeline:psalgu_boundary_comparison) can run headless in batch scripts or via qgis_process. The graphical review dock panel is loaded lazily and activates only when QGIS is running with a graphical user interface (iface).