The map runs out before the country does
· 9 min read
For about a month our resolver used one method. It takes a postcode, finds the city polygon that contains the postcode's centroid, and reads off the city. The method got the Netherlands to 95% and Germany to 93%. Then we ran it on Japan, and Japan's gazetteer data has no city polygons.
This post covers two countries where the gazetteer data is sparse, what a geocoder can still do there, and where it stops. We resolved Japan to 94% by replacing the polygon lookup with a postal-authority lookup. Korea had the opposite problem. We could place the coordinate correctly for every postcode, but we could not confirm the name of the place most of the time.
The work raised three questions:
- What do you do when the gazetteer gives you points where you expected shapes?
- Does the method that worked for Japan generalize, or did it work only once?
- What happens when the map is missing data for the part of a country you most need?