Finnish observations of Soviets shelling their own troops on the Karelian Isthmus 26.11.1939. Four days later Soviet Union declared war on Finland using this as a pretext.
The map portrays observation posts Finnish troops used to identify the
locations of the artillery strikes. The arrows from different posts
indicate bearings to the observations, using Finnish military radians
where a full circle is 6000. 1500 or 15-00 indicates east.