Points of interest
A point of interest or POI is a feature on a map (or in a geodataset) that occupies a particular point, as opposed to linear features like roads or areas of landuse. A point of interest is not necessarily very interesting, so, for example, post boxes are relatively interesting/uninteresting, depending on context and your subjective opinion. The term POI is actually quite imprecise, but is widely recognised by users of satellite navigation systems (SATNAVs), who are often presented with options to show or hide points of interest. It's also for geocaching and GIS users, but "POI" takes on different meanings in different GIS systems.
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
POIs in OpenStreetMap
OpenStreetMap has an element type: node which has geographic coordinates. Nodes are certainly used to represent POIs, but 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.
We will need to look at the tags of nodes to see what type of POI is being represented, and perhaps we can regard any node which has tags applied to it, as a POI. Most nodes which are just part of way, do not have tags applied to them (tags are applied to the way), but a node for a railway crossing will have a tag: railway=crossing. The Map Features page gives a list of common tags used (but not all)
This is still not the full story, because features which we might think of as POIs are in some cases (and increasingly more frequently with the availability of more high resolution imagery) drawn as areas. 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.
- One feature, one OSM element
- Mapping techniques
- 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.)
- Upload Waypoints
- Tool for extracting POIs from OSM binary files
- HTTP API to query POIs extracted from OSM planet file