12+Times Asked
~50Total Marks
6Topics
MediumPriority
1 GIS Data Sources
- Primary: Field surveys, GPS, total station, remote sensing, photogrammetry.
- Secondary: Existing maps, census data, reports, scanned documents.
- Digital: Satellite imagery (Landsat, SPOT), existing GIS databases, web services (WMS/WFS).
2 Location vs Topological Errors
- Location errors: Positional inaccuracy — wrong coordinates (e.g., feature shifted, poor GPS accuracy).
- Topological errors: Structural mistakes — dangling nodes, overshoots, undershoots, slivers, gaps, overlapping polygons.
3 Direct vs Indirect Data Capture
- Direct (primary): Data collected specifically for the project. GPS survey, field measurement, new satellite image acquisition.
- Indirect (secondary): Data originally collected for another purpose. Digitising existing paper maps, downloading census data, scanning aerial photos.
4 Metadata
"Data about data." Describes content, quality, condition, and access of spatial data.
- Includes: source, date, accuracy, projection, scale, data format, responsible organisation.
- Standards: ISO 19115 (geographic metadata), FGDC (US standard).
- Purpose: data sharing, quality assessment, preventing misuse, long-term archival.
5 Data Quality Parameters
- Positional accuracy: How close coordinates are to true locations.
- Attribute accuracy: Correctness of non-spatial information.
- Logical consistency: Valid topology, no contradictions.
- Completeness: All features and attributes present.
- Temporal accuracy: Data up-to-date for intended use.
- Lineage: History of data — sources, transformations, processing steps.
6 GPS Integration Steps
- Plan survey (accuracy requirements, coordinate system).
- Collect GPS data with attributes in field.
- Apply differential correction.
- Transfer to computer.
- Coordinate transformation if needed.
- Import into GIS, overlay with existing layers.
Past Exam Questions
+What are the data sources for GIS? (2071, 2073, 2076, 2081)
Primary (GPS, survey, RS), Secondary (maps, census), Digital (satellite, web). Classify and give 2 examples each.
+Differentiate location errors and topological errors. (2074, 2078)
Location: positional shift. Topological: dangling nodes, overshoots, undershoots, slivers, gaps. Draw diagrams of each error type.
+What is metadata? Why is it important in GIS? (2075, 2079, 2080)
"Data about data." Contents: source, date, projection, accuracy, format. Importance: sharing, quality assessment, preventing misuse. Standards: ISO 19115.
+Explain data quality parameters. (2072, 2076)
Six parameters: positional accuracy, attribute accuracy, logical consistency, completeness, temporal accuracy, lineage. One example each.
+How are GPS data integrated into GIS? (2071, 2074)
Six steps: plan, collect, differential correction, transfer, transform coordinates, import and overlay.