AI-ASSISTED · EDITOR-REVIEWED

Theme brief

Invert land and water, foreground and background, north and south, or the map and its margin. The reversal should expose an assumption in ordinary maps, not merely make the viewer work harder.

Official prompt
“Inside out, upside down. Something on this map is not quite right.”
30DayMapChallenge 2026

02

WAYS IN

Four map ideas

01
Treat oceans as countries and land as negative space.
02
Make a south-up map and examine which labels suddenly feel wrong.
03
Map a city from the perspective of its underground infrastructure.
04
Turn a boundary map into one about the shared edges rather than the enclosed areas.

03

IN THE DIRECTORY

Recommended tools

QGIS

Inverted polygon fills, blend modes and geometry generators support visual reversals.

Open source · View details

Mapshaper

Useful for erasing, dissolving and rebuilding land-water geometry.

Open source · View details

D3 (d3-geo)

Enables custom clipping and projection experiments in code.

Open source · View details

geojson.io

Good for quickly inspecting whether the transformed geometry still works.

Free · 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 Natural Earth physical vectors

Coasts, land, oceans, rivers and other small-scale reference layers.

Public domain OpenStreetMap base data

Follow the tile provider policy as well as the database attribution rules.

ODbL 1.0 · attribution required

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

Keep one familiar anchor — a label, graticule or coastline — so the reversal can be understood rather than merely decoded.

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