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9. Buffers

Goal: Master the Buffer tool — make polygons at a fixed distance around features.

What buffer does

Input point ●            Buffer 500m       ▢
                  ──→         ⬭

Input line  ─────         Buffer 100m   ▭▭▭▭▭

Input polygon ▭          Buffer 100m   ▢▢▢

Tool location

Geoprocessing pane → Search "Buffer" → Buffer (Analysis Tools).

Parameters

Parameter Notes
Input Features Layer to buffer
Output Feature Class Where to save (in the project gdb)
Distance Number + unit, OR a field with per-feature distance
Side Type FULL, LEFT, RIGHT, OUTSIDE_ONLY (lines/polygons)
End Type ROUND, FLAT (lines)
Method PLANAR or GEODESIC
Dissolve Type NONE, ALL, LIST

Distance: number vs field

  • Number — same buffer for everything (e.g., 500 meters)
  • Field — variable distance per feature. E.g., a BUFFER_M field with different radii for different fire stations.

Planar vs geodesic

Method When
Planar Layer is in a projected CRS (UTM, State Plane). Fast, accurate locally.
Geodesic Layer is in a geographic CRS (lat/long), or you're buffering across very large distances. Computes great-circle.

If your buffer looks oddly shaped

You're probably buffering lat/long with PLANAR. Either project the data first (preferred) or use GEODESIC.

Dissolve types

  • NONE — every input feature gets its own buffer polygon (overlapping zones stay separate).
  • ALL — all buffers merge into one big polygon.
  • LIST — merge buffers that share an attribute value.
Use case Dissolve type
"Service zones — keep separate per facility" NONE
"Total area within 500 m of any fire station" ALL
"Zones grouped by district" LIST

Multi-ring buffer

Need 100, 250, 500 m at once? Use Multiple Ring Buffer (Analysis Tools) instead. Output gets a distance field for each ring.

Common patterns

Workflow Distance Side Dissolve
School proximity zones 1 mi FULL NONE
Riparian buffer along streams 30 m FULL ALL
Setback inside a parcel 10 m OUTSIDE_ONLY NONE
Highway noise zone 200 m LEFT/RIGHT NONE
Fire station service-area approximation 1 mi FULL ALL

After the buffer

Buffers are usually a step, not the answer. Follow up with:

  • Clip — crop other layers to the buffer
  • Spatial Join — count features inside each buffer
  • Intersect — calculate overlap with other polygons

Practice

Park access analysis

  1. Add a parks layer (polygons).
  2. Project to State Plane.
  3. Buffer 0.5 mi (FULL, ALL).
  4. Spatial Join the buffer to census blocks → count blocks within 0.5 mi.
  5. Calculate the % of city population with park access.

→ Next: Clip.