Analysis and Geoprocessing
Core concepts
Geoprocessing tools read inputs, apply an operation, and write outputs. Understand tool parameters, environments (workspace, output coordinate system, extent, mask, cell size), and the difference between overwrite behavior and creating new outputs. Know common tools by purpose: Buffer, Clip, Intersect, Union, Dissolve, Spatial Join, Select by Location, and Project. Distinguish attribute queries from spatial queries. Understand ModelBuilder as a way to chain tools into a repeatable workflow and Python as the scripting equivalent.
Traps to watch for
- Clip cuts features to a boundary; Intersect keeps overlapping geometry from all inputs; Union keeps all areas.
- Environments can silently change output - extent and mask alter raster results.
- Spatial Join transfers attributes by spatial relationship; it does not merge geometry.
- Dissolve aggregates by attribute and can compute statistics.
- Running a tool with an existing output name may overwrite unless overwrite is disabled.
Worked example / rule of thumb
To count how many schools fall inside each district, use Spatial Join with the within relationship and a one-to-many or summarize option, or Select by Location followed by a summary. Rule of thumb: ask what the output geometry should be - if it should be trimmed to a boundary, Clip; if combined, Union or Intersect.