From open data to spatial insight.

Acquisition and normalisation

Overpass retrieves OSM nodes, ways and relations. Nodes retain their coordinates; ways and relations use centre points. Invalid records are skipped, missing metadata remains null, and OSM type plus ID prevents duplicate imports.

State scope and district aggregation

PostGIS ST_Covers assigns facilities to the Penang state polygon and five DOSM district polygons. One district match assigns a district; multiple matches remain ambiguous. Original OSM tags remain preserved. Map filters, dashboard counts, nearest and radius queries share this scope. Simplified coastline geometry and facility centre points can affect membership.

Spatial measurements

The public Sites edition uses a fixed OSM/DOSM snapshot exported from the verified PostGIS database. GeographicLib computes WGS84 ellipsoidal inverse distances in metres in the browser. Nearest results sort by distance then facility ID; radius inclusion uses distance <= radius. A 128-vertex geodesic circle illustrates the radius. State and district assignments were computed in PostGIS before export. Updates require republishing a new snapshot; this edition has no live PostGIS server.

Interpretation and limitations

Distances are straight-line measures. OSM completeness varies; counts do not establish capacity, service quality or public access. Published DOSM polygons are an analysis reference rather than a cadastral determination. An accessibility index remains planned and no validated score is calculated.