Choropleth Map

Color geographic regions by a data value. Works with GeoJSON and GeoDjango.

When to Use

• Visualizing a metric across regions (risk scores, population, revenue)
• Any GeoJSON FeatureCollection with a numeric property

With GeoDjango

from d3_bridge import ChoroplethMap

chart = ChoroplethMap(
    geodata=AdminBoundary.objects.filter(level=2),
    value_field="deforestation_risk",
    tooltip=["name", "area_ha", "risk_score"],
    projection="mercator",
    center=[-5.5, 7.5],
    title="Deforestation Risk",
)

The GeoQuerySet is automatically serialized to GeoJSON.

With Raw GeoJSON

import json

with open("regions.geojson") as f:
    geojson = json.load(f)

chart = ChoroplethMap(
    geodata=geojson,
    value_field="gdp_per_capita",
    title="GDP per Capita",
)

Color Scales

# Sequential (default) — light to dark
chart = ChoroplethMap(geodata=qs, value_field="value", color_scale="sequential")

# Diverging — red-yellow-green
chart = ChoroplethMap(geodata=qs, value_field="value", color_scale="diverging")

# Threshold — discrete buckets
chart = ChoroplethMap(
    geodata=qs, value_field="value",
    color_scale="threshold",
    color_domain=[10, 25, 50, 75, 90],
)

Parameters

Parameter	Type	Default	Description
geodata	GeoQuerySet or dict	—	GeoJSON data source
value_field	str	—	Property to color by
geometry_field	str	None	Geometry field name (auto-detected)
properties	list	None	Fields to include in GeoJSON properties
projection	str	"mercator"	"mercator", "albers", "naturalEarth", "equirectangular", "orthographic"
center	list	None	[longitude, latitude] center point
scale	float	None	Projection scale
color_scale	str	"sequential"	"sequential", "diverging", "threshold"
color_domain	list	None	Thresholds for threshold scale
stroke_color	str	"#fff"	Border color
stroke_width	float	0.5	Border width
null_color	str	"#ccc"	Color for missing values
zoom	bool	True	Enable zoom/pan