Geoprocessing Tools¶

Goal: Master the everyday geoprocessing tools that power 80% of GIS analysis.

What you'll learn

The "big 5" geoprocessing tools: Buffer, Clip, Intersect, Union, Dissolve
When to use each
How they differ from each other

The big 5¶

flowchart LR
    B[Buffer] -.expand.-> Result1[New polygons<br/>around features]
    C[Clip] -.cookie cutter.-> Result2[Features inside<br/>boundary only]
    I[Intersect] -.overlap only.-> Result3[Where layers<br/>overlap]
    U[Union] -.combine all.-> Result4[All features<br/>preserved]
    D[Dissolve] -.merge.-> Result5[Combine by<br/>shared attribute]

    classDef tool fill:#4338ca,stroke:#312e81,color:#fff,font-weight:bold
    class B,C,I,U,D tool
    classDef out fill:#dcfce7,stroke:#10b981,color:#065f46
    class Result1,Result2,Result3,Result4,Result5 out

Buffer¶

Creates a polygon around features at a specified distance.

Use case
"All schools within 500 m of a major road"
"Service area for a fire station"
"Riparian buffer 30 m from streams"

Inputs: features, distance, units. Output: polygon layer.

Always project first

Buffer needs distance. If your layer is in a geographic CRS (lat/long), the result will be wrong. Project to a projected CRS (UTM, State Plane) first.

→ See Buffers.

Clip¶

Cuts an input layer using a clip layer (the "cookie cutter").

Use case
"Get only the streets inside Fulton County"
"Crop a satellite image to a watershed boundary"

Inputs: input features, clip features. Output: input features, but only the parts inside the clip boundary.

→ See Clip.

Intersect¶

Computes the geometric overlap of two or more layers, AND combines their attributes.

Use case
"Parcels that fall in the floodplain — and tag each one with the flood zone code"
"Forest patches inside National Parks — keeping both attributes"

Inputs: two or more layers. Output: only the overlapping geometry, with attributes from all input layers joined.

→ See Intersect.

Union¶

Combines two layers — keeps everything from both, plus computes overlap.

Use case
"Combine zoning + floodplain into a single layer with all attributes preserved"

Output: every piece of geometry, with attributes from one or both layers.

Dissolve¶

Merges features that share an attribute value.

Use case
"Merge all census tracts in the same county into county-level polygons"
"Combine all 'Forest' land cover patches into one feature"

Inputs: features, dissolve field. Output: fewer, larger features.

→ See Dissolve.

Quick comparison: Clip vs Intersect¶

	Clip	Intersect
Purpose	Crop one layer using another's boundary	Find overlap and combine attributes
Output attributes	Only from the input layer	From all input layers
Common use	"Trim to study area"	"Tag features with what they overlap"

Quick comparison: Dissolve vs Union¶

	Dissolve	Union
Inputs	One layer	Two or more layers
Result	Fewer, larger features (merged by attribute)	Same or more features (combined geometry)

Other essential tools¶

Erase / Symmetric Difference

Remove parts of one layer that overlap another.
Multipart to Singlepart

Split a multipart feature into separate features.
Merge / Append

Combine multiple layers of the same geometry type into one.
Generate Near Table

Find the nearest neighbor between layers, with distance.
Minimum Bounding Geometry

Get the convex hull or bounding box of a feature.
Create Fishnet / Tessellation

Build regular grids (squares, hexagons) for analysis.

ModelBuilder & Python¶

Once you've combined a few tools into a workflow, automate it:

ModelBuilder — drag-and-drop visual workflow editor in ArcGIS Pro.
Python (arcpy) — write the workflow as a script. → Python for GIS.

import arcpy
arcpy.analysis.Buffer(
    in_features="schools.shp",
    out_feature_class="schools_buffer.shp",
    buffer_distance_or_field="500 Meters"
)

Practice¶

Buffer + Clip + Intersect chain

Buffer hospitals by 1 mile.
Clip the buffers to your county boundary.
Intersect those buffers with census tracts.
Calculate the population inside each buffer.

You just measured hospital service-area population — a real GIS deliverable.

Next up¶

→ Cartography & Map Design — make those analyses look professional.