http://wiki.openstreetmap.org/wiki/Notes

Notes is a new (04/23/2013) feature of the OpenStreetMap.org website. Visitors can now “Add a note” to the map in order to easily mark errors in the map data. This feature is only intended for discussions about the map data, and not for general purpose notes like “I was here on Saturday” or “There was a crime at this location”. All notes are always publicly visible to anyone. To submit a new note, or comment on a note, it is not necessary to log-in or have an OSM account, but it is beneficial to do so. Notes are intended as a two way communication, and the ability for a mapper to ask for more details if necessary to resolve the issue is important. Logged-in users will automatically get an email notification if comments were added to a note or the issue was resolved.

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