A hydrologist needs to model water flow across a landscape. Should the elevation data be stored as vector contour lines or a raster DEM?
AVector contour lines, because they show elevation more precisely
BA raster DEM, because flow algorithms require a continuous grid where each cell has a defined elevation, slope, and flow direction to its neighbors
CEither format works equally well for flow modeling
DVector points at surveyed locations, interpolated on the fly during analysis
Hydrological flow modeling algorithms (D8, D-infinity) operate on raster grids, calculating flow direction from each cell to its lowest neighbor. This requires every location to have a defined elevation. Vector contours only represent elevation at specific intervals, leaving gaps between contours where elevation is undefined. The raster DEM provides the continuous elevation surface that flow algorithms require.
Question 2 True / False
Vector data is always more accurate than raster data for representing geographic features.
TTrue
FFalse
Answer: False
Accuracy depends on the data source and the phenomenon being represented, not the data model. A high-resolution raster (1 m cells) may represent boundaries more accurately than a generalized vector dataset digitized from a 1:100,000 map. For continuous phenomena like elevation or temperature, raster is the natural representation; forcing these into vector format (contours) actually loses information. Each model suits different phenomena and analyses.
Question 3 Short Answer
Explain the concept of topology in vector GIS data and why it matters for spatial analysis.
Think about your answer, then reveal below.
Model answer: Topology defines the spatial relationships between features: which polygons share boundaries, which lines connect at nodes, which polygons are adjacent. Without topology, polygons might overlap or have gaps at shared boundaries, lines might fail to connect at intersections, and adjacent features might have inconsistent boundaries. Topology rules enforce data integrity (no gaps, no overlaps, shared boundaries stored once) and enable spatial queries that depend on connectivity and adjacency -- like finding all parcels adjacent to a given parcel, or tracing connected river segments from source to mouth.
Topology transforms a collection of independent geometric shapes into a structured spatial network where relationships between features are explicitly defined and maintained.