Spatial Data Infrastructure (SDI), OGC Standards & Metadata

Explanation

Historically, individual government ministries duplicate surveying efforts, producing conflicting maps of the same territory. A National Spatial Data Infrastructure (NSDI) establishes a centralized geoportal where agencies publish metadata catalogs and share live data services over OGC protocols. WMS delivers rendered map image tiles (PNG/JPEG) for fast web display, while WFS allows client GIS software to download, edit, and analyze actual vector vertices and attribute fields across the internet.

Key points

• SDI Core Components: People/Institutions, Policies & Legal agreements, Access Networks/Clearinghouses, Spatial Data, and Standards.
• Geospatial Metadata: 'Data about data'; documents provenance, coordinate system, spatial extent, accuracy, lineage, and usage restrictions (ISO 19115 standard).
• Open Geospatial Consortium (OGC) Web Services: WMS (Web Map Service - serves map image tiles), WFS (Web Feature Service - serves raw vector geometry and attributes), WCS (Web Coverage Service - serves raw raster data).
• OpenStreetMap (OSM): Global collaborative open-data mapping project providing crowd-sourced geospatial vector data under Open Database License (ODbL).

Example

Code examples

<!-- Standard OGC Web Feature Service (WFS) Request -->
GET /geoserver/wfs?
  service=WFS&
  version=2.0.0&
  request=GetFeature&
  typeNames=nepal:district_boundaries&
  outputFormat=application/json
  HTTP/1.1
Host: geoportal.gov.np

Exam questions

• [8 Marks] Explain the concept and core components of Spatial Data Infrastructure (SDI). What is the role of metadata (ISO 19115)?
• [7 Marks] Differentiate between OGC Web Map Service (WMS) and Web Feature Service (WFS) with their respective use cases.