AI-ASSISTED · EDITOR-REVIEWED

Theme brief

Polygons describe areas, but their apparent size can dominate the story. Decide whether area is the subject or merely a container for a rate, category or texture, and never map raw counts as a choropleth when the population at risk varies.

Official prompt
“A map challenge classic. Map with polygons.”
30DayMapChallenge 2026

02

WAYS IN

Four map ideas

01
Compare park access across neighbourhoods with a restrained choropleth.
02
Turn building footprints into a figure-ground portrait of a city.
03
Map watershed boundaries instead of political boundaries.
04
Distort familiar administrative areas into a value-by-area cartogram.

03

IN THE DIRECTORY

Recommended tools

QGIS

Handles joins, classification, topology checks and publication-quality polygon styling.

Open source · View details

Mapshaper

Excellent for simplifying heavy boundaries and repairing common geometry problems.

Open source · View details

geojson.io

Lets you inspect and hand-edit a small GeoJSON polygon in the browser.

Free · View details

Datawrapper

A quick option for a clean, responsive choropleth with a clear legend.

Freemium · View details

04

START WITH A CLEAR LICENSE

Data sources

Natural Earth administrative areas

Generalized world boundaries at multiple scales; read boundary notes.

Public domain OpenStreetMap building footprints

Coverage and tagging detail vary by place.

ODbL 1.0 · attribution required geoBoundaries

Open administrative boundaries with standardized metadata.

CC BY 4.0 for open release

Licenses are a planning aid, not legal advice. Check the source record and version you actually download; terms can vary within a catalog.

05

BEFORE YOU EXPORT

Cartography check

Normalize counts into a rate or ratio before choosing a color scale, then state the denominator in the legend.

06

COMMUNITY MAPS

Selected work

Selections begin after this theme closes.

First participate officially by posting publicly with #30DayMapChallenge. You can then suggest that original post for our independent MapTools picks. We link to the source, credit every author and use images only with permission.

Suggest for MapTools picks