Domain 2: Spatial Analysis and Modeling
Domain 2 tests spatial analysis and modeling: selecting features, combining layers, measuring proximity, analyzing rasters, and building defensible suitability models. Questions emphasize correct units, appropriate tools, and whether an analysis answers the stated question.
Vector analysis
Attribute queries filter rows by fields; spatial queries filter by location. Overlay tools differ: clip cuts input to a boundary; intersect keeps overlapping geometry from both layers; union keeps all extents; erase removes the erase feature. Spatial joins transfer attributes by a specified relationship (intersects, within, contains) and can aggregate one-to-many matches with count, sum, or mean. Buffers need a projected CRS in linear units; network distance requires network analysis, not Euclidean buffering.
Raster analysis
Map algebra combines rasters cell by cell. Reclassification converts continuous values to classes, and distance tools produce Euclidean or cost surfaces. Interpolation (IDW, spline, kriging) estimates surfaces from sample points; kriging explicitly models spatial autocorrelation through a variogram. Terrain tools derive slope, aspect, and hillshade from a DEM; slope units and vertical exaggeration must be checked.
Worked example
Find sites within 500 m of a road, with slope under 10%, outside a floodplain. Project roads and the slope raster to a metric CRS. Buffer roads at 500 m. Reclassify slope to 1 (0–10%) and 0 (>10%). Convert the floodplain polygon to a raster mask with 0 inside and 1 outside. Multiply the three rasters with map algebra; cells equal to 1 are candidates. Count candidate cells and multiply by cell area to report hectares. Document thresholds and cell size because both change the result.
Traps
- Buffering in a geographic CRS, producing ellipses measured in degrees.
- Confusing intersect with union or clip.
- Treating a cost surface as straight-line distance.
- Ignoring the modifiable areal unit problem when aggregating to polygons.
- Selecting only by attribute when the question requires a spatial relationship.