The <a href="https://en.wikipedia.org/wiki/Maidenhead_Locator_System" class="extiw" title="en:Maidenhead Locator System">Maidenhead Locator System</a> grid over Europe. The areas marked with big letters are "fields" and the small numbers denote "squares".
Oona Räisänen (<a href="https://en.wikipedia.org/wiki/User:Mysid" class="extiw" title="w:User:Mysid">Mysid</a>)
CC BY-SA 3.0
Base map from <a href="//commons.wikimedia.org/wiki/File:Blank_map_of_Europe_(polar_stereographic_projection)_cropped.svg" class="mw-redirect" title="File:Blank map of Europe (polar stereographic projection) cropped.svg">Image:Blank map of Europe (polar stereographic projection) cropped.svg</a>; Grid drawn in Inkscape and based on the (public domain) output of Great Circle Maps v2.3.