Land cover data provide the basis for FRAP analyses of wildlife habitat, water, grazing, and development impacts. No single mapping effort provides GIS data adequate to address this broad range of issues. Efforts to map land cover statewide typically provide insufficient resolution to capture types that occur as "inclusions", such as wet meadows, riparian areas, or certain types of development. Other efforts tend to focus on mapping land cover for a specific geographic area (e.g. bioregion, national park), or theme (e.g. wetlands, farmland). Since resources were targeted to a narrow focus, many of these efforts can make a reasonable claim to be the "best" for their respective area or theme. In order to provide the most solid basis for our analyses, FRAP staff made the decision to take advantage of these sources and merge them into a single GIS data layer.

Merging data from multiple sources required addressing differences in scale, resolution, and consistency. In addition, each data source had to be cross-walked into a common classification system ( California Wildlife Habitat Relationships, CWHR).