Over 900 attendees were at the Free and Open Source Software for Geospatial (FOSS4G) conference in Portland this year. Last year's FOSS4G 2013 in Nottingham attracted 833 delegates. This year's attendance matches Denver's FOSS4G in 2011 record.
There are also equally successsful regional FOSS4G conferences, most notably FOSS4G-Asia which just took place in Bangkok, Thailand and FOSS4G North America 2015 which is coming up at the San Francisco Airport Hyatt Mar 9-12.
Next year's FOSS4G 2015 will be hosted in Seoul (South Korea) Sep 14-19.