Project 1 — Population Choropleth Map¶

Goal¶

"How is population density distributed across [your state]'s counties, and which counties are growing or shrinking?"

Build a clean, normalized choropleth showing population density at the county level, with an optional second panel showing percent change since 2010.

Data needed¶

ArcGIS Living Atlas alternatives:

• "USA Counties (Generalized)" — geometry + 2020 population
• "ACS Population Variables - Boundaries" — recent ACS

Tools used¶

• ArcGIS Pro: Add Join, Calculate Field, Symbology (Graduated Colors)
• SQL: WHERE clauses for state filter
• Layout: title, legend, scale bar, north arrow, source

Step-by-step workflow¶

Step 1 — Set up¶

1. Create project population_choropleth_<state>.
2. Add a folder connection to your data folder.
3. Set the map's CRS to NAD83 / Conus Albers (EPSG:5070) for area accuracy.

Step 2 — Add and filter¶

1. Add the US counties layer.
2. Definition Query: STATEFP = '13' (Georgia) — adjust to your state.

Step 3 — Join population data¶

1. Add the ACS table.
2. Validate the FIPS field type matches.
3. Right-click counties → Add Join on FIPS.
4. Export to a permanent feature class once joined.

Step 4 — Normalize¶

You want density, not raw count.

1. Open the attribute table.
2. Add field: POP_DENSITY (Double).
3. Calculate: !POP2020! / (!Shape_Area! * 0.000001) (m² → km²).

(Or use Calculate Geometry → Area to populate AREA_KM2 first, then divide.)

Step 5 — (Optional) Compute % change¶

1. Add field POP_CHANGE_PCT (Double).
2. Calculate: ((!POP2020! - !POP2010!) / !POP2010!) * 100.

Step 6 — Symbology¶

Two maps. Build them in two separate maps for clean comparison.

Map A — Density¶

1. Symbology = Graduated Colors on POP_DENSITY.
2. Method = Quantile (good for skewed density data).
3. Classes = 5.
4. Color scheme = sequential blue.
5. Round legend labels: <50, 50–200, 200–500, 500–2000, >2000.

Map B — Change¶

1. Symbology = Graduated Colors on POP_CHANGE_PCT.
2. Method = Manual Interval: <-5, -5 – 0, 0 – 5, 5 – 15, >15.
3. Color scheme = Diverging (RdBu) — declines red, growth blue.
4. Make sure 0 maps to the white middle of the diverging palette.

Step 7 — Layout¶

1. Insert → Layout → Tabloid Landscape (11×17) — gives room for two map panels.
2. Two map frames side by side.
3. Shared elements: title, source, projection note.
4. Per-frame: legend, scale bar.
5. Title: "Population Density and Change, [State] Counties, 2010–2020".

→ Detailed checklist: Professional Map Layout.

Step 8 — Export and ship¶

1. Export to PDF (vector, 300 dpi).
2. Export a PNG (150 dpi) for your portfolio site.
3. Push the project + write-up to a GitHub repo.

Skills learned¶

• Tabular joins
• Field calculation
• Graduated color symbology
• Sequential vs diverging palettes
• Multi-map layouts
• Professional export

Portfolio value¶

This is the easiest project to ship and the hardest to do well. Most beginner choropleths fail one of: normalization, palette, classification, layout. Doing all four right is a strong signal.

Stretch goals¶

• Add a dot density layer underneath showing absolute population.
• Animate the change over multiple decades using ArcGIS Pro's time-aware layers.
• Build a small ArcGIS Online dashboard with a map + bar chart of top/bottom counties.

→ Next: Transit Desert Analysis.