An important element in the matching process, is the location. Different sources give different locations for the same pont of interest, of course, but they shouldn't be radically different if they're really talking about the same place.
|Source||Average distance to OSM|
|Lonely Planet||51.6 meters|
As we see the distance is smallest for Facebook - which means the coordinates of Facebook places are more like the ones found in the OpenStreetMap than in any of the other sources. So we thought let's have a look how many points of interest have a distance that's under 1 meter. In other words: which percentages of all points of interest have the same coordinates. We don't need a table for this. The answer is 15% of all Facebook points of interest have almost exactly the same coordinates as the OpenStreetMap. For other sources this is under 1%. Wow. You can hardly call this a coincidence.
|Foto CC by Roger and Renate Rossing|
For a moment there we thought that Facebook was copying OpenStreetMap coordinates (which is allowed) without crediting the OpenStreetMap (which is not allowed). But before making any (wild) accusations we dug a bit deeper. We looked at how much the coordinates matched in different countries. And it seemed that most of the difference we saw between Facebook and the others was explained by one country: the United States. In the US alone a whopping 37% of the coordinates of Facebook were exactly the same as the ones found on the OpenStreetMap.
If Facebook had really been using OpenStreetMap to seed their Places database with good coordinates, why had they only done it for the US? There had to be a better explanation. And there is. Unlike any of the other sources OpenStreetMap actually shows where coordinates come from (they don't make them up either). We checked some ten points of interest that had exactly the same coordinates and found all of them had one single source: GNIS So both OpenStreetMap and Facebook use GNIS for their location database.
And GNIS is free to use, for all, without the need to mention where it's from. It also explains why every single church in the US is on Facebook Places - it's not just because Americans like to check in every Sunday morning.