An environmental agency needs to identify wetlands within 1 km of a highway that also fall within a designated conservation zone. Which sequence of spatial operations accomplishes this?
AGeocode the highway, then reclassify the wetland raster
BBuffer the highway by 1 km, then intersect the buffer with both the wetland layer and the conservation zone layer
CMerge all three layers into a single dataset and filter by attribute
DCalculate NDVI for the highway corridor
Buffering creates a 1 km zone around the highway. Intersection is the overlay operation that identifies areas where all three conditions overlap: within the buffer, classified as wetland, and within the conservation zone. This is the fundamental GIS workflow for multi-criteria site selection.
Question 2 True / False
Tobler's First Law of Geography states that everything is related to everything else, but near things are more related than distant things. This principle is irrelevant to modern spatial analysis.
TTrue
FFalse
Answer: False
Tobler's First Law is foundational to spatial analysis. It underlies spatial autocorrelation (why nearby measurements tend to be similar), interpolation (why we can estimate unknown values from nearby known values), and geostatistics (kriging explicitly models the distance-dependence of correlation). Spatial analysis techniques that ignore this principle produce unreliable results.
Question 3 Short Answer
Explain the difference between a buffer operation and a Thiessen (Voronoi) polygon operation, and give one application of each.
Think about your answer, then reveal below.
Model answer: A buffer creates a zone of specified distance around features (e.g., 500m buffer around a pollution source to define an impact zone). A Thiessen/Voronoi polygon partitions space so that every location is assigned to its nearest input point, creating polygons where all points inside are closer to that polygon's generator than to any other. Application: buffers define exclusion zones, impact areas, or service areas at fixed distances. Thiessen polygons define service territories (e.g., assigning each address to its nearest school or hospital based on straight-line proximity).
Buffers are distance-from-feature operations; Thiessen polygons are nearest-neighbor-assignment operations. Both answer proximity questions but in fundamentally different ways.