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How to make a choropleth map

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A choropleth map is one of the most effective ways to visualize data across geographic regions. By shading areas such as districts, states, or countries based on data values, these maps help reveal patterns and trends at a glance.

With Atlas, creating a choropleth map is simple, even if you're new to GIS tools. Follow this step-by-step guide to learn how.

What Is a Choropleth Map?

A choropleth map displays data using shaded or colored regions to represent different values. The shading corresponds to a dataset, making it easy to compare values across geographic areas.

Examples of Choropleth Maps:

  • Population density by region.
  • Average income by state.
  • COVID-19 cases per country.
  • Land use percentage in districts.

Step 1: Prepare Your Data

To create a choropleth map, you’ll need:

  1. Geographic Data with Boundaries: If your dataset already includes boundaries (e.g., polygons representing districts or states), you’re ready to go. These files may come in formats like GeoJSON or Shapefiles.
  2. Attribute Data: If your dataset doesn't already include boundaries, you’ll need a separate boundary file (e.g., GeoJSON or Shapefile) and a dataset with the values you want to visualize. These two datasets can be joined based on a shared column, like region name or code.

Step 2: Log In and Set Up Your Project

  1. Log In to Atlas: Open your web browser and log in to your Atlas account.
  2. Create a New Project: Click the New Project button to start your map.
  3. Name Your Project: Give it a descriptive title like “Choropleth Map of Population Density.”

Step 3: Add Data and Upload Files

  1. Go to Add Data: In the top-left corner, click the Add Data button.
  2. Upload Your Data:
    • If your dataset already includes boundaries, simply upload the file (e.g., GeoJSON or Shapefile).
    • If using separate files, upload both the boundary file and the attribute file containing the values you want to visualize.

Step 4: Style Your Choropleth Map

  1. Select the Boundary Layer: In the Layers Panel, click on the boundary layer you uploaded.
  2. Go to Standard Styling:
    • Open the styling options for the layer and navigate to the Standard Styling section.
  3. Choose Fill Style:
    • In the fill settings, select Style by Field.
    • Choose the field from your dataset that you want to use for styling (e.g., population, household income, or cases per region).
  4. Adjust the Color Palette:
    • Select a color palette:
      • Sequential: Best for ordered data (e.g., low to high population).
      • Diverging: Ideal for datasets with a midpoint (e.g., income relative to the national average).
      • Qualitative: Use for categorical data (e.g., land use types).
    • Adjust the number of steps to control how many color ranges appear on the map (e.g., 5 for broad categories, 10 for detailed visualization).
  5. Refine the Fill:
    • Adjust the opacity of the fill color to make the map more or less transparent.
  6. Customize the Outline:
    • Set the outline style, such as a thin white border, to separate regions clearly without overwhelming the map.

Step 5: Analyze the Map

  1. Interpret Patterns:
    • Examine the shading to identify trends. For example, darker areas may show higher values (e.g., high population density or high income).
  2. Overlay Additional Data:
    • Add layers for context, such as infrastructure, roads, or points of interest, to compare with the choropleth map.

Step 6: Add Interactivity

Make your map more engaging by adding interactivity, including filters in Builder mode:

  1. Enable Pop-Ups:
    • Configure pop-ups to show details when clicking on a region. For example:
      • Region name.
      • Exact value (e.g., population density or income).
  2. Add Filters in Builder Mode:
    • Switch to Builder Mode in Atlas.
    • Add a Filter Widget to your project:
      • Choose the field to filter (e.g., population, income, or category).
      • Define filter options:
        • Range Slider: For numeric values like population or density, allow users to set a minimum and maximum range.
        • Dropdown Menu: For categorical data like land use or income groups, let users select specific categories.
    • Style the filter widget and position it in the interface for easy user access.
    • Test the filters to ensure they work as expected. Adjust settings if necessary to make the filtering smooth and intuitive.

Step 7: Finalize and Share Your Map

  1. Style and Polish:
    • Add a title, legend, and any necessary labels to ensure your map is clear and professional.
    • Ensure the filters and pop-ups are working smoothly.
  2. Export Options:
    • Export your map as a high-quality image, PDF, or an interactive web map.
  3. Share Your Map:
    • Use Atlas’ sharing options to make your map public with a link, share it with your workspace, or embed the map directly into a website.

Practical Applications of Choropleth Maps

  • Urban Planning: Analyze population density or infrastructure needs by district.
  • Health Studies: Visualize the spread of diseases or healthcare access by region.
  • Market Analysis: Compare customer demographics or income levels across locations.
  • Environmental Studies: Show land use or pollution levels by area.

Tips for Creating Effective Choropleth Maps

  • Use Accurate Data: Double-check your data for errors or inconsistencies.
  • Choose Clear Color Schemes: Avoid overly complex palettes. Use intuitive colors for better readability (e.g., blue for low values, red for high values).
  • Simplify Where Possible: Focus on one variable at a time to avoid clutter.
  • Test Your Map: Share the map with a small group for feedback before publishing.

With Atlas, creating and sharing a choropleth map is a powerful way to turn data into actionable insights. Whether you're using interactive filters, styling by field, or highlighting trends, Atlas helps you tell a visual story that engages and informs.

Start your choropleth map project in Atlas today and bring your data to life!