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It's a referenced plus-code, which "saves" 4 digits. Instead of being a true location like the full plus code, coordinates, or MGRS, a referenced plus-code req

It's a referenced plus-code, which "saves" 4 digits. Instead of being a true location like the full plus code, coordinates, or MGRS, a referenced plus-code requires a referenced location to resolve (think "124 meters north of the postal office"), and the precision becomes entirely dependent on the precision of the services used to resolve the reference location (i.e. Google Maps might consider the exact location for "Honolulu" to be somewhere else on the island of Honolulu than Bing Maps).

detaro 8y ago
No, they do not work relative to a point. You replace the first 4 digits of the code (the area code) with a location name that's clearly in the area, the following digits stay the same. The name resolution of the location can be off by kilometers and it still works.
- arghwhat 8y ago
  While you are correct in stating that the point is only used to resolve the area, you conclusion is off by kilometers (he he he). When using a point to resolve a 4-digit code (1x1 degree, approx 100x100km), it is true that anywhere within the same 4-digit-equivalent area will result in the same location. However, while this improves the average case compared to point referencing, it makes the worst case absolutely horrendous: You'll end up referring to a wrong long/lat degree, meaning an error of over 100km! The closer you are to the edge of a lat/long degree, the more vulnerable you are. If your location is, say, 10 meters from the edge, then 10 meters geocoding imprecision is all it takes to cause a >100km error. Which is exactly why the plus-code readme says the following, as I have quoted before: > If the reference location is derived from a town or city name, it is dependent on the accuracy of the geocoding service. Although one service may place "Zurich" close to the Google office, another may move it by a hundred meters or more, and this could be enough to prevent the original code being recovered. Rather than a large city size feature to generate the reference location, it is better to use smaller, neighbourhood features, that will not have as much variation in their geocode results. In order for the reference system to work, references must either be close to the center of a lat/long degree (which allows great error margins on geocoding), or use points which have consistently high precision. Neither case result in memorable reference codes like "XYZ Honolulu", so just using the extra 4 digits is the only sensible choice.

detaro 8y ago

No, they do not work relative to a point. You replace the first 4 digits of the code (the area code) with a location name that's clearly in the area, the following digits stay the same. The name resolution of the location can be off by kilometers and it still works.

arghwhat 8y ago
While you are correct in stating that the point is only used to resolve the area, you conclusion is off by kilometers (he he he). When using a point to resolve a 4-digit code (1x1 degree, approx 100x100km), it is true that anywhere within the same 4-digit-equivalent area will result in the same location. However, while this improves the average case compared to point referencing, it makes the worst case absolutely horrendous: You'll end up referring to a wrong long/lat degree, meaning an error of over 100km! The closer you are to the edge of a lat/long degree, the more vulnerable you are. If your location is, say, 10 meters from the edge, then 10 meters geocoding imprecision is all it takes to cause a >100km error. Which is exactly why the plus-code readme says the following, as I have quoted before: > If the reference location is derived from a town or city name, it is dependent on the accuracy of the geocoding service. Although one service may place "Zurich" close to the Google office, another may move it by a hundred meters or more, and this could be enough to prevent the original code being recovered. Rather than a large city size feature to generate the reference location, it is better to use smaller, neighbourhood features, that will not have as much variation in their geocode results. In order for the reference system to work, references must either be close to the center of a lat/long degree (which allows great error margins on geocoding), or use points which have consistently high precision. Neither case result in memorable reference codes like "XYZ Honolulu", so just using the extra 4 digits is the only sensible choice.