Points of interest
A point of interest (POI for short) is a term used in cartography (and therefore in reference to maps or geodatasets) for the choice to represent a particular feature using an icon that occupies a particular point. The idea is that, as opposed to linear features like roads or areas of landuse, some features might be suited to being indicated as a point in a particular context; for example, if one wanted to send a letter, it would be relevant to see all the post offices and mailboxes nearby, and if they are all represented by an envelope icon, it is easy to see . There are five factors[1] that distinguish high-quality POI data: freshness, coverage, consistency, ease of use and customization.
Three caveats:
- A POI does not necessarily have to be stored as a point in a geodatabase (see #In OSM for details particular to us); it merely is represented as a point in the user interface (for example, in the standard tile layer).
- Do not take the 'of interest' part too literally; a feature might be quite ordinary, such as the postboxes mentioned above, and only in the context of the map user wanting to mail something does it become "interesting". As such, POIs are often amenity=*s.
- The flavours of usage of the term may vary between users of satellite navigation systems (SATNAVs), geocachers, and GIS users, but the gist is basically as defined above.
Some example of types of POI:
- Churches, schools, town halls, distinctive buildings
- Post offices, shops, postboxes, telephone boxes
- Pubs (pub names are useful when navigating by map)
- Car parks and lay-bys (and whether free or not)
- Speed cameras
- Tourist attractions
In OSM
To reiterate the first caveat above, POI features need not be mapped as a point. In OpenStreetMap, any of the elements are fair game: node is obvious, but ways (which can be closed [cyclic] or open, filled [as an area] or unfilled) or even a relation (usually just as a multipolygon) may be better suited for the individual feature. These objects have tags which describe the feature they represent.
Just as POIs are not always nodes, nodes are not always (or even usually) POIs: the concepts don't map directly across. For example nodes are also used as part of ways to represent linear features. You might regard all standalone nodes (nodes that are not part of a way) as representing points of interest; however, a point of interest can actually be part of the way, for instance, a railway level crossing.
POIs are drawn as areas in some cases (and increasingly more frequently with the availability of more high resolution imagery). Data users might try to simplify areas down to a centroid point. Provided mappers have followed the One feature, one OSM element mapping practice, this should work reasonably well.
POIs from OpenStreetMap on my device
Some devices (satnavs, GPS units, smartphone apps) will support display of POIs provided you can load them in the required format. Particularly in the case of SATNAVs, map data is often represented using encryption, which allows the manufacturer control to prevent you loading any data (free OpenStreetMap data) onto your device. And you thought you owned it! Interestingly though some such devices will allow POI data to be overlayed in a more open fashion.
To find out how to load POI data from OpenStreetMap onto your device (or whether its possible to do so) you can hopefully find some helpful information on the wiki. Look for your brand of device, e.g., linked from the GPS Reviews page. In the absence of any information (Please help add this to the wiki!) you should investigate features for displaying POIs, or "waypoints". There may be files on the storage media, or procedures for transferring data onto the device by USB cable.
In some cases POI files are available as prepared downloads.
See also
- One feature, one OSM element
- Map Features
- Elements
- Contribute map data
- Wikipedia2Go
- Openlayers POI layer example — Explains how to show POI markers on an OSM slippy map by using an overlay layer
- W3C Working Draft specification for a POIs standard (There is no known OSM software related to this yet.)
- Tool for extracting POIs from OSM binary files
- OpenPoiMap
- OpenMarkers — a bit dead (underlying OSM map has not been updated for a long time), but otherwise useful.
- OsmPoisPbf is a Java based tool for scanning an OpenStreetMap file for nodes and areas (and relations) whose tags indicate them as POIs (points of interest) and extracts those into a comma separated file (CSV).