Spatial/GIS
Spatial/GIS
This domain tests the management and analysis of spatial data in support of surveying and land information. It covers coordinate reference systems, vector and raster models, metadata, topology, overlay analysis and data governance.
Core rules and concepts
- Every spatial layer needs a defined coordinate reference system; NZTM2000 is common for New Zealand metric work, while geographic coordinates are in degrees.
- Vector data represent discrete features; raster data represent continuous surfaces such as elevation or imagery.
- Metadata records source, accuracy, currency, lineage and licensing; without it, a layer cannot be judged fit for purpose.
- Topology rules catch gaps, overlaps and dangling nodes before analysis.
- Spatial joins and overlays depend on consistent CRS, scale and attribution.
Worked example
You must find parcels within 100 m of a stream. Project both layers to NZTM2000, buffer the stream by 100 m, intersect the buffer with the parcel layer, then sum the selected parcel areas. Buffering in geographic coordinates would treat degrees as metres and produce a meaningless distance. The reasoning is: the analysis distance is metric, so the CRS must be metric; the overlay then transfers stream proximity to parcels. Check for multipart parcels, overlaps and slivers before reporting the area.
Traps
Buffering in latitude/longitude; mixing CRS or datums; trusting a layer without metadata; ignoring topology errors; reporting false precision from a coarse source; and using licensed data outside its terms.