This is a flag design for the proposed nation of Cascadia. This flag was designed by Andrew Rogers, and you can read more about Cascadia and his flag designs at andrewrogers.net.
Cascadia is a proposed nation which would consist of the current British Columbia, Washington, and Oregon. There are also many proposed flags for this could-be nation. The most popular one can be found on the Wikipedian Casacadia article, but I think it looks way too much like the flag of Lesotho, and the black evergreen just does not make any sense at all.
This design by Andrew Rogers is simple and symbolic. The seven five-pointed stars represent the "seven original commonwealths that formed the kingdom". The green is the color of evergeens, which are very easy to find in "Cascadia". You can find more of Andrew Rogers' designs at this website.