Facebook Places and their coordinates

To make our travel guides we crawl a number of sources for travel information. The next step is to match the points of interest from these different sources on each other. This is quite complicated. OpenStreetMap may call the San Francisco Museum of Modern Art "SF MOMA" and wikitravel may call it "SFMOMA" - our job is to find out if they are talking about the same thing. We do this both for open content sources as well as copyrighted sources, such as Lonely Planet - but for these last sources we don't use the actual content of course, we just use them for reference.

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.

If we look at how far the coordinates from a sources for its points of interest are from the coordinates of OpenStreetMap we get the following overview:

Source	Average distance to OSM
TripAdvisor	65.8 meters
Facebook	43.8 meters
Lonely Planet	51.6 meters
Frommer's	75.7 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.