HIST289

Visualizing HOLC Redlining Data in QGIS - Columbus

Lab Instructions: Creating a Redlining Map

This exercise will guide you through downloading HOLC redlining data and creating a professional map using QGIS. You’ll work with both vector data (boundaries) and raster data (historical maps).

Step 0: Download and Organize Data

Download Data from Mapping Inequality

1. Go to Mapping Inequality
2. Navigate to the Columbus, Ohio map
3. Important: Scroll down past the initial download buttons at the top of the page
   • The buttons at the top download the entire national dataset (all cities)
   • You need the individual city data shown as thumbnails below
4. Find the Columbus, Ohio thumbnails showing both vector and raster data previews
5. Download the Geopackage format for vector data (recommended for beginners)
6. Download the GeoTIFF raster file for the historical map background
7. Rename the files to columbus.gpkg and OH_Columbus_1936.tif respectively

Why Geopackage vs GeoJSON?

• Geopackage (.gpkg): Single file, handles complex data better, industry standard, works perfectly in QGIS
• GeoJSON (.json): Text-based, web-friendly, but can be larger and slower for complex datasets
• Shapefile (.shp): Legacy format that requires multiple files (.shp, .shx, .dbf, .prj) - you’ll likely encounter these in other courses or professional work, but they’re more complicated for beginners
• For beginners: Use Geopackage - it’s more reliable and faster in QGIS

Files You Should Have:

• [cityname]_boundaries.gpkg - Vector file containing HOLC redlining boundaries with grade classifications
• [cityname]_1936.tif - Historical raster map from 1936

Understanding HOLC Grades:

• Grade A (Best/Green): Lowest risk areas for lending
• Grade B (Still Desirable/Blue): Moderate risk areas
• Grade C (Declining/Yellow): Higher risk areas
• Grade D (Hazardous/Red): Highest risk, often minority neighborhoods

Step-by-Step Instructions

Step 1: Load Data into QGIS

1. Open QGIS and create a new project
2. Add the raster layer:
   • Go to Layer → Add Layer → Add Raster Layer
   • Browse and select your [cityname]_1936.tif file
   • Click Add and Close
3. Add the vector layer:
   • Go to Layer → Add Layer → Add Vector Layer
   • Browse and select your [cityname]_boundaries.gpkg file
   • Click Add and Close

Step 2: Add a Base Map

1. Install QuickMapServices plugin (if not already installed):
   • Go to Plugins → Manage and Install Plugins
   • Search for “QuickMapServices” and install
2. Add base map:
   • Go to Web → QuickMapServices → OpenStreetMap → OSM Standard
   • Or try Google → Google Satellite for aerial imagery

Step 3: Style the HOLC Boundaries by Grade

1. Right-click on your boundaries layer (e.g., columbus_boundaries) → Properties
2. Go to Symbology tab
3. Change from “Single Symbol” to “Categorized”
4. Set Value to “grade” (this is the field containing A, B, C, D classifications)
5. Click “Classify” to automatically create categories
6. Customize colors for each grade:
   • Grade A: Green (#228B22 or similar)
   • Grade B: Blue (#4682B4 or similar)
   • Grade C: Yellow (#FFD700 or similar)
   • Grade D: Red (#DC143C or similar)
7. Adjust transparency to ~30-50% so you can see the base map underneath
8. Click OK to apply

Step 4: Add Labels to Show Area Names

1. Right-click on your boundaries layer → Properties
2. Go to Labels tab
3. Change from “No Labels” to “Single Labels”
4. Set Value to “label” (this contains A1, A2, B1, etc.)
5. Customize label appearance:
   • Increase font size (12-14pt recommended)
   • Choose a contrasting color (black or white)
   • Add a white halo or buffer for better readability
6. Click OK to apply

Step 5: Organize Layer Order

1. In the Layers panel, drag layers to organize:
   • Boundaries layer (vector) - on top
   • Base map (web layer) - middle
   • Historical map (raster) - bottom (optional, can turn off)

Step 6: Save Your Work

1. Save the project:
   • Project → Save As
   • Choose a location and filename (e.g., “[CityName]_Redlining_Map.qgz”)
2. Export a map image:
   • Project → Import/Export → Export Map to Image
   • Choose PNG or JPEG format
   • Set resolution (300 DPI for high quality)
   • Click Save

Recommended Color Schemes

Traditional HOLC Colors:

• A: #76a865 (green)
• B: #7cb5bd (blue)
• C: #ffff00 (yellow)
• D: #d9838d (red/pink)

High Contrast:

• A: #228B22 (forest green)
• B: #4682B4 (steel blue)
• C: #FFD700 (gold)
• D: #DC143C (crimson)

Colorblind Friendly:

• A: #2E8B57 (sea green)
• B: #4682B4 (steel blue)
• C: #DAA520 (goldenrod)
• D: #B22222 (fire brick)

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GeoJSON vs Geopackage vs Shapefile: Key Differences

Geopackage (.gpkg) - RECOMMENDED

• Single file format (easy to share and manage)
• Industry standard for modern GIS workflows
• Excellent performance with large datasets
• Supports complex data types and relationships
• Cross-platform compatibility

GeoJSON (.json)

• Human-readable text format
• Web-friendly - works directly in web browsers
• Good for simple datasets and web mapping
• Can be large for complex geometries

Shapefile (.shp)

• Legacy format - still widely used
• Multiple files required (.shp, .shx, .dbf, .prj minimum)
• Performance issues with large datasets
• Limited data types and field name restrictions

When to Use Each:

• Use Geopackage for most GIS work, especially as a beginner
• Use GeoJSON for web mapping and simple data sharing
• Use Shapefile only when required by older software or specific workflows