AI-ASSISTED · EDITOR-REVIEWED
Theme brief
NULL is not zero. It may mean missing, suppressed, not applicable, not collected or lost during processing; a map can expose those distinctions instead of silently dropping records or painting them with the lowest value.
Official prompt“NULL”
30DayMapChallenge 2026
WAYS IN
Four map ideas
- 01
Send invalid coordinates to Null Island and explain why they gather there.
- 02
Map where a public dataset has no observations.
- 03
Compare “zero events” with “no reporting system.”
- 04
Visualize the records removed at each step of a geocoding workflow.
IN THE DIRECTORY
Recommended tools
QGIS
Expression rules make NULL, zero and empty strings visibly distinct.
Open source · View detailsDuckDB Spatial
Audits missing coordinates and geometry problems across large files quickly.
Open source · View detailsGeoPandas
Makes a reproducible data-quality map in a concise Python workflow.
Open source · View detailsgeojson.io
Useful for inspecting malformed or unexpectedly empty features.
Free · View detailsSTART WITH A CLEAR LICENSE
Data sources
Document the collection method, date and privacy decisions.
You choose the license OpenStreetMap quality and completenessUse change and validation tools to study missing or inconsistent features.
ODbL 1.0 for OSM data GBIF occurrence recordsFilter by license and cite the download DOI when available.
CC0, CC BY or CC BY-NC per recordLicenses are a planning aid, not legal advice. Check the source record and version you actually download; terms can vary within a catalog.
BEFORE YOU EXPORT
Cartography check
Write a legend entry for every kind of absence. If you cannot explain why a value is missing, call it unknown rather than zero.
COMMUNITY MAPS
Selected work
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