Location vs. Place vs. POI

With Nokia, Google, Facebook and a whole host of other players recognising the inherent value in the concept of Places and Points Of Interest (POIs), it’s good to see that the World Wide Web Consortium (W3C), the standards body of the Web, is getting involved. On the 30th. September 2010, the W3C Points Of Interest Working Group (POIWG) was launched with a “mission to develop technical specifications for representation of POI information on the Web”. I should pause to make a brief disclaimer here; I’m sitting on the POIWG as part of my day job with Ovi Places at Nokia.

Of course, in order to develop those technical specifications, we need to define what a POI is in the first place. There’s a lot of acronyms flying around (3 in the first paragraph of this post alone) and a lot of conflicting terminology further confusing the matter. Even the most cursory of glances through Web content on this topic shows the terms Place, Location and POI being used interchangably and so as part of the discussion I tried to codify the difference between, and most importantly the inter-relationships between, these three seemingly straightforward terms. The genesis for this post first appeared on the POIWG public mailing list last week (and W3C working groups conduct their business as much as possible in public) but I’ve fleshed it out in a bit more detail here.

Locations vs. Places vs. POIs

So what is a POI? … Wikipedia defines a POI as a Point Of Interest … a “specific point location that someone may find useful or interesting”. But we really need a more subtle and complex definition.

To my mind, a POI is part of a loosely coupled and inter-related geographical terms, comprised of (in generalised order of scope and granularity) Locations, POIs and Places.

A Location is a geographical construct; a physical fixed point on the surface of the Earth. It could also be used to describe a fixed point on the surface of another celestial body but for the purposes of this Working Group, we’ll restrict the scope to terrestrial geographies. A Location is described by a centroid (a longitude and latitude in a widely adopted system, such as WGS-84) and an extent, either a Minimum Bounding Rectangle or a vector set. A Location is temporally persistent, it does not generally change over time.

A POI is a human construct, describing what can be found at a Location. As such a POI typically has a fine level of spatial granularity. A POI has the following attributes …

  1. A name
  2. A current Location (see the commentary below on the loose coupling of POI and Location)
  3. A category and/or type
  4. A unique identifier
  5. A URI
  6. An address
  7. Contact information

A POI has a loose coupling with a Location; in other words, a POI can move. When this occurs, the loose coupling with the previous location is removed and, providing the POI continues to exist, it is then coupled with its new Location. This can happen when the human activity at the POI relocates, such as when your local coffee shop relocates to a new address. It’s still your local coffee shop, it’s now found at a different Location.

A POI has temporal boundaries; it starts when the human activity at that Location commences and ends when human activity ceases, such as when a company or organisation goes out of business.

And then there’s a Place, which is also a human construct and typically has a coarse level of spatial granularity. Places are typically larger scale administrative constructs, either informally or formally defined. Countries, States, Counties, Districts, Neighbourhoods and postal codes or telephone area codes are all Places. Places are also informally or colloquially defined, such as the Home Counties in the United Kingdom and The Bay Area in the United States.

Places have spatial relationships; with parents, children, adjacencies and “contained by” semantics. Places also have the same attribute set as POIs, although with differing interpretations based on scale; for example, the address of a Place or its URI would refer to the address of the administrative or governing body of the Place.

A Place typically contains multiple POIs and can also be coterminous with a POI. In the former case, a Place, such as a city or a neighbourhood, will contain multiple POIs. In the latter case, a Place and a POI will occupy the same position and extent, such as in the case of Yellowstone National Park, which is both a Place and a POI.

As discussions in the POIWG get deeper and deeper into what constitutes a POI and, equally importantly, what doesn’t, it’ll be interesting to see how much of my take on the subject survives.

Written and posted from the BA North Lounge, Heathrow Airport, Terminal 5 (51.474161, -0.484344)

10 Comments

  • as seems to me for most applications like foursquare, fb places etc. Place == POI. It there any reason to make them different?

  • To further confuse the terminology and discussion, I think the WG also needs to consider a class of POIs and places that is not permanently tied to any specific geographical location because people tend to refer to such places frequently and without much regard for whether the exact centroid of the place is readily available or not.

    I’m thinking of indoor places/pois where the physical location or centroid is likely unknown (or at least undocumented) but its position relative to something else might be well known (e.g. Gary’s desk, against the wall, corner room, fourth floor, Schoenhauser Allee 180, Berlin). These places tend to move as well, as we found out the hard week last weekend :-).

    Another, different class of places/pois are those that are on the move: train carriages, restaurants on a cruise ship, ferries, etc where the place is relative to a moving object like a ship, train, airplane, etc.

    You might exclude such relative places to keep things simple but I think they actually constitute the bulk of the interesting places at the really fine grained level, which generally are note geo-referenced. Ultimately, you don’t want to check in to your airport terminal but to the little coffee shop near gate 42.

    People don’t think in terms of coordinates and vectors but in more relative terms. I think place and poi models should account for that. The job of geo-referencing this information against e.g. the WGS-84 grid (including height, of course) is a key challenge. But most of this information is useful without being geo-referenced. Do you really need to know the centroid of your desk in order to find it? Would it be helpful to have that centroid? I’m not so sure that is essential.

  • [...] This post was mentioned on Twitter by Gary Gale, Erik Wilde. Erik Wilde said: RT @vicchi: New Bloggage: Location vs. Place vs. POI – http://vtny.org/D9 [...]

  • I would think issues pertaining to scale and representation of features (‘points’ (rarely are genuinely points), lines and polygons are all represented as points of interest depending on the scale at which they are being represented) would be important in informing the discussion. This doesn’t eliminate at all the need for the URI to link to the geography/vector set of the feature that different users will want to use and represent in different ways.
    Another thought: as a human construct Place is vernacular with boundaries fluid both over time and across different communities.

  • It should also be made clear that this definition of “POI” deliberately limits itself to things in the physical world. While the importance of the physical world will always be great, it is still continuously decreasing.

  • @Den: For check-in based apps and services putting Place and POI in the same bucket certainly makes sense but despite the amount of press coverage, check-ins are far from the sole use case for Places, Locations and POI. At the micro end of the scale Place and POI are going to be colocated and synonymous but as you widen the scope towards the macro end of the scale you see POIs being contained within Places. While I can just about see people checking-in to, say, a neighbourhood, I don’t imagine many people would want to check-in to a city, or a County, or a State or a Country. It’s for this reason that I separate out Place and POI.

  • @Jilles: I think for indoor POIs the model still works; granted, there’s (currently) a lack of widely used ways to geocode such sites but that’s more down to the lack of sensor data rather than a need to make a sub-class of micro-POI or indoor-POI.

    As to moveable POIs, whilst I see no reason against creating such POIs, I can’t (as yet) see a use case above and beyond creating them (and probably checking-in to them).

  • @Holger: Thinking of geocoding virtual worlds? Or extra-terrestrial worlds? You’d need a good coordinate system for the former.

  • @Gary: the problem for indoor is wider than just a lack of sensor data (or rather usable, feasible & cost effective indoor positioning technology). There’s simply a lack of data on what buildings look like (e.g. floor plans), what’s inside them and where, and how all this information relates to the real world (geo-referencing). The information what latitude, longitude, and altitude stuff has is fairly meaningless if you can’t put it on a map, navigate to it, or do nearby searches. We’re decades away from solving that in my opinion.

    Yet, most of the interesting places in this world are indoors. I.e. the best results of a search for something are likely to be indoors and should have sufficient granularity for the user to find it in the real world. Street addresses and their outdoor GPS coordinates are not that useful in large locations like airport terminals, office buildings, shopping malls. You typically need something beyond that in order to find stuff.

    That something is missing in the definition above. However, I agree, you could probably shoehorn some of the essentials in it.

  • ‘Interest’ is surely in the eye of the beholder, just like beauty and art. Maybe there should curators for POIs, just like in the art world, who decide what is a POI and what isn’t, based on a combination of history, knowledge and subjectivity.

    As a next step these curators could then specialize in niche POI areas – baroque, renaissance, pop, punk, classical, postmodern arty farty, etc

    :)