The Leaflet Choropleth module provides advanced choropleth mapping capabilities for Drupal applications, enabling the visualization of statistical data through color-coded geographic regions. This module seamlessly integrates with the existing Drupal Leaflet and Geofield ecosystem to deliver professional-grade thematic mapping functionality.

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Installation

Composer Installation

composer require drupal/leaflet_choropleth

Module Installation

Via Drupal Admin UI:

1. Navigate to /admin/modules
2. Search for "Leaflet Choropleth"
3. Check the module checkbox
4. Click "Install"

Via Drush:

drush en leaflet_choropleth

Configuration and Usage

View Style Integration

The module provides a leaflet_choropleth_map view style plugin that integrates seamlessly with the leaflet_map view style from the Leaflet module and its "leaflet_view" submodule. This integration adds and enables an additional "Choropleth Map Settings" section where to configure choropleth-specific settings alongside standard leaflet mapping options.

Usage requirements and setup

The choropleth visualization applies only to features with polygon or multipolygon geometry types.

To enable a choropleth map for your data, follow these steps:

• create a leaflet_choropleth_map view that includes Drupal content or entities with a numeric field (integer or float) to be used as the basis for the choropleth data visualization.
  Note: Of course first you need to set the Geofield filed type that should drive the Leaflet Map (@see the Leaflet & Leaflet Views module instructions)
• in the "Choropleth Map Settings" section enable the Choroplath Map option and set the data source to the desired numeric field
• configure additional settings such as classification methods, color scale, number of classes, geometries display options, legend configuration and other display preferences

Classifications and Color Ranges

The module implements a robust plugin system for data classification and color schemes:

Classification Methods:

• Equal Interval: Divides data into equal-sized ranges
• Geometric Interval: Creates class breaks based on geometric progression
• Natural Breaks (Jenks): Optimizes class boundaries to minimize variance
• Quantile: Divides data into equal-sized groups
• Standard Deviation: Classes based on statistical deviation from mean
• Etc: additional classification methods (custom implementations) available through the plugin system

Color Ranges:

• Sequential: Single-hue progressions (Blues, Greens, Reds, Grays)
• Diverging: Two-color endpoints with neutral midpoint (Red-Blue)
• Categorical: Distinct colors for categorical data (hint: refer to the leaflet_choropleth.api.php file and the leaflet_choropleth_color_scale_alter hook for suggestion on how to accomplish this)
• Etc: additional color ranges (custom implementations) available through the plugin system

Legend Configuration

The module provides a configurable legend system that can be:

• Added as a Leaflet Control directly within the map
• Positioned anywhere on the map interface
• Fully customized for styling and content
• Integrated with the choropleth theming system

Theming Integration

Leaflet choropleth layers can be seamlessly integrated and mixed with existing leaflet mapping features, allowing for:

• Combining choropleth analysis with marker & geometries visualizations
• Multi-layer mapping compositions, with flexible theming and styling options

Dependencies

• Leaflet module (& its Leaflet Views submodule)

Development Status and Roadmap

The Leaflet Choropleth module is being developed and deployed to the Drupal community for testing and review, with the intention of eventual integration into the main Leaflet module as a leaflet_choropleth submodule once thoroughly validated and consolidated by the community.