Marin County Parks is surveying the boundary of the Gary Giacomini Open Space Preserve, providing county agencies with a reference point for future projects that might require an understanding of property encroachments, defensible spaces and other factors. The project, a portion of which is complete, began in 2017. Max Korten, the parks department’s director and general manager, said the San Geronimo Valley preserve has particularly complex property boundaries and winding canyons; one-time surveys are more cost-effective than surveying every time a new project pops up, he added. The county, which allotted an additional $237,000 for the project last week, is planning to survey 34 open space preserves.