Georeferencing Guide
A practical summary based on Georeferencing Best Practices (Chapman & Wieczorek, 2020) — read in ~2 minutes.
What is georeferencing?
Georeferencing is the process of interpreting a textual locality description — such as "5 km NW of Ratanakiri, Cambodia" — into a geographic coordinate pair (latitude/longitude) plus a coordinate uncertainty radius that captures the imprecision of the original description.
The result is not just a point on a map, but a point-radius: the true location lies somewhere within a circle centered on the given coordinates.
Step-by-step
Read the full label
Use all available fields — locality, state/province, country, collector, date, habitat. They provide context to disambiguate place names.
Find the named place
Use a gazetteer (Google Maps, GeoNames, Getty Thesaurus of Geographic Names) to locate the feature described. Prefer historical gazetteers when the collection is old — place names change.
Place the coordinate
For a named feature, use its center. For directional descriptions ("5 km NW of [town]"), find the town's center and apply the heading and distance to get the georeference point. For administrative areas with no finer detail, use the centroid.
Estimate the uncertainty
The uncertainty radius must encompass every possible true location. It combines: the extent of the named feature, the precision of any distance/direction given, and GPS/map accuracy. When in doubt, go larger — underestimating uncertainty is worse than overestimating it.
Document your sources and remarks
Note which gazetteer or tool you used and any assumptions you made. This allows future reviewers to verify or improve the georeference.
Uncertainty quick reference
| Locality description | Typical uncertainty |
|---|---|
| GPS coordinates on label | 10–100 m |
| Named village or small town | 1–5 km |
| "5 km NW of [town]" | Geographic radial of town + imprecision of distance/direction |
| Named river, lake or mountain | Radius of smallest circle enclosing the feature |
| County / district only | Radius of the administrative area |
| Country only | Radius of the country |
When to skip
- The locality is too vague to narrow down below country level.
- Multiple equally plausible interpretations exist and you cannot resolve the ambiguity.
- The place name is unresolvable in any gazetteer, even with contextual clues.
In these cases it is better to leave it ungeoreferenced than to assign misleading coordinates.
Further reading
- Georeferencing Best Practices — Chapman AD & Wieczorek JR (2020). GBIF Secretariat. The authoritative reference.
- Georeferencing Quick Reference Guide — Zermoglio PF, Chapman AD, Wieczorek JR, Luna MC & Bloom DA (2020). GBIF Secretariat. Step-by-step worked examples.
- Georeferencing Calculator Manual — Bloom DA, Wieczorek JR & Zermoglio PF (2020). GBIF Secretariat.
Ready to put this into practice?
Start georeferencing →