Glossary of Wildfire, Water, Drone, and Imaging Terms
Plain definitions of the terms HOAs, cities, property owners, and their advisors meet when working with aerial documentation, each with a source.
Wildfire rules, water rules, drone regulations, and imaging terms come with their own vocabulary. This glossary defines the terms that come up most when HOAs, cities, property owners, and their advisors work with aerial documentation. Most terms link to an official or academic source, or to a FlyCRE guide that covers them in depth.
Wildfire and vegetation rules
Defensible space
The managed area between a building and the vegetation around it, kept to slow a fire's spread, reduce ember and heat exposure, and give firefighters room to work. CAL FIRE describes it in zones extending out to 100 feet (CAL FIRE).
Zone 0 (ember-resistant zone)
The first 5 feet around a structure, where state law calls for keeping out materials that embers can ignite. The Board of Forestry adopted emergency Zone 0 regulations on August 19, 2026 (Best Best & Krieger), but the package was withdrawn from state review on September 8, 2026, so no statewide Zone 0 rule is in effect yet; see our Zone 0 status guide for where it stands.
Fuel modification zone
A band of land next to development where vegetation is permanently managed to reduce fire risk. In OCFA areas the standard zone is 170 feet wide, in Zones A through D. See the Orange County fuel modification guide.
Fuel modification plan
The plan OCFA approves for a project's fuel modification zones, showing zone layout, plant choices, and who maintains each area. Once installed, the zones must be maintained permanently (OCFA Guideline C-05).
Fire Hazard Severity Zone (FHSZ)
A State Fire Marshal map classification, Moderate, High, or Very High, based on the physical fire hazard of an area over the long term. It does not reflect mitigation work on individual properties (Office of the State Fire Marshal).
Very High Fire Hazard Severity Zone
The highest of the three hazard classes. The state released updated maps for local responsibility areas in early 2025 (Office of the State Fire Marshal).
Local Responsibility Area (LRA)
Land where a city or county, not the state, is responsible for wildfire protection. Local fire hazard severity zone maps cover these areas (Office of the State Fire Marshal).
State Responsibility Area (SRA)
Land where the state is financially responsible for wildfire protection. State defensible space requirements under PRC 4291 apply to structures in the SRA (PRC 4291).
Wildland Urban Interface (WUI)
The zone where homes and other development meet or mix with burnable wildland vegetation (U.S. Fire Administration).
PRC 4291
The California law that requires defensible space around structures in the State Responsibility Area, including the ember-resistant zone closest to the structure (PRC 4291).
AB 38 (defensible space at sale)
The law requiring sellers of homes in High or Very High Fire Hazard Severity Zones to give buyers documentation of a defensible space inspection where the local agency runs an inspection program, codified in Civil Code section 1102.19. In OCFA areas, OCFA performs these inspections (OCFA FAQ).
Insurance and community programs
Firewise USA
A National Fire Protection Association program that helps neighborhoods organize and act to live more safely with wildfire (NFPA).
Fire Risk Reduction Community
A city, county, or district recognized by the Board of Forestry for meeting fire planning best practices. The 2026 list took effect July 1, 2026 (Board of Forestry).
Safer from Wildfires
A California Department of Insurance framework that requires insurers to offer discounts for wildfire mitigation at the structure, the property, and the community level (California Department of Insurance).
California FAIR Plan
California's insurer of last resort for property owners who cannot find coverage in the regular market. It is funded by the state's licensed property insurers (California FAIR Plan).
Drone rules
Part 107
The FAA rule for commercial drone operations with aircraft under 55 pounds. It requires a remote pilot certificate, a registered aircraft, and Remote ID compliance (FAA).
Part 107 waiver
FAA approval to fly outside specific Part 107 limits, such as beyond visual line of sight or over people. Applications go through the FAA's online system (FAA).
LAANC
The Low Altitude Authorization and Notification Capability, an FAA and industry system that gives near real-time approval to fly below 400 feet in controlled airspace near airports (FAA).
Remote ID
A drone's broadcast of its identity and location while in flight, required for drones that must be registered (FAA).
TFR (temporary flight restriction)
A temporary no-fly area published by the FAA, often over wildfires and major events. Drones may not fly in one without permission from the controlling agency (FAA).
BVLOS
Beyond visual line of sight: flying a drone farther than the pilot can see it unaided. Under Part 107 it requires a waiver (FAA).
Part 108 (proposed)
A proposed FAA rule, published August 7, 2025, that would create a standard path for beyond visual line of sight operations. It is not final (Federal Register).
FCC Covered List
An FCC list of communications equipment deemed a national security risk. Listed equipment cannot receive new FCC authorizations. See our FCC drone rules explainer (FCC).
Imaging terms
Orthomosaic
An orthophoto mosaic: many overlapping aerial photos stitched into one image and corrected so that distances read true, like a map (Penn State).
Digital surface model (DSM)
An elevation model that includes everything on the ground, such as roofs and tree canopy, rather than bare earth alone.
Photogrammetry and 3D models
Photogrammetry is the science of taking measurements from photographs. Overlapping images are combined to build 3D models of terrain and structures (Penn State).
Ground sample distance (GSD)
The ground size of one pixel in an image. A smaller GSD means finer detail. For drones, it depends on flight altitude and the camera.
Georeferencing
Tying imagery to real-world coordinates so it lines up with maps and with earlier captures (Penn State).
RGB imagery
Ordinary color imagery made from the red, green, and blue bands of visible light (Penn State).
Thermal imagery
Imagery that records the infrared energy surfaces give off, shown so that temperature differences are visible (NASA). It records surface temperature, not causes.
Multispectral imagery
Imagery that records reflected light in several separate wavelength bands, often including near-infrared light the eye cannot see (Penn State).
NDVI
The Normalized Difference Vegetation Index, calculated from near-infrared and red reflectance to map vegetation greenness (USGS).
NDRE
The Normalized Difference Red Edge index, similar to NDVI but using red-edge light, a narrow band between red and near-infrared.
Asset visibility
FlyCRE's close-range imagery layer for specific features such as drainage, access roads, and rooftop equipment, captured alongside the orthomosaic. See the platform.
Water and landscape
Nonfunctional turf
Turf that is not used for recreation or community activities, such as grass in street medians and parking areas. State law phases out watering it with drinking water for public, commercial, and HOA properties (Water Code 10608.12). See our turf ban deadlines post.
CII water use
Water used by commercial, industrial, and institutional customers, such as businesses, manufacturers, schools, and government facilities (State Water Board FAQ).
Large landscape
Under California's conservation regulation, a commercial, industrial, or institutional landscape of half an acre or more on a mixed-use meter (State Water Board FAQ).
Property and legal
Property condition assessment
A commercial due diligence survey under ASTM E2018, combining a walk-through by a field observer with records research and producing a property condition report (ASTM International). It is different from aerial documentation; see inspection or documentation?
SB 326 and SB 721
California laws requiring periodic inspection of elevated balconies, decks, and stairways by qualified inspectors: SB 326 for condominium associations and SB 721 for apartment buildings with three or more units (City of San Ramon).
Reserve study
An HOA's study of its major components and the funds needed to repair and replace them. California Civil Code section 5550 requires a visual inspection at least every three years and an annual review (Civil Code 5550).
Chain of custody
A record of who collected, held, and transferred evidence, and when (NIST). For how FlyCRE handles records, see the attorneys page.
Image metadata
Information stored inside an image file, such as camera settings, in standard formats like EXIF (Library of Congress).
Definitions are summaries for general reference as of October 21, 2026, not legal advice. Follow the linked official sources for current requirements.