SW Regional GAP Analysis

  1. Contact information for the data set: South West Regional Gap Analysis
  2. General location of data set: AZ, CO, NV, NM, UT (5-state region)
  3. General landscape type: Biodiversity of the entire region
  4. Number of reference samples: Approximately 93,000 samples, about half from field sampling.
  5. Approximate area over which samples are distributed: 560,000 mi2.
  6. Response design: 1 ha plot (minimum)
  7. Sampling design: Primarily opportunistically, along roads.
  8. Attributes recorded for each sample: Plot data were collected using ocular estimates of biotic and abiotic land cover elements, including percent cover of dominant species by life form (i.e. trees, shrubs, grasses, and forbs) and physical data such as elevation, slope, aspect and landform.
  9. How attributes were determined:
    • Half of the samples are ground data, which were collected primarily through field work.
    • Field samples were collected by traversing navigable roads in a mapping zone and opportunistically selecting plots that met criteria of appropriate size (1-hectare minimum) and composition (stand homogeneity).
    • Laptop computers using ArcView software, Landsat imagery, digital orthophoto quads, and other ancillary information were also used for navigation and plot identification whenever possible.
    • Each plot was identified with a paired UTM coordinate using a GPS and a visually interpreted polygon representing the survey plot. Generally two digital photos were taken at each plot.
    • Field data were recorded onto hardcopy field forms and subsequently entered into a database.
    • Sufficient data were collected to assign a NVC alliance (Grossman et al. 1998) and/or ecological system (Comer et al. 2003) label to each plot.
    • Samples collected via air photo interpretation (3 % of total) were collected exclusively by the Utah team.
    • Samples collected via DOQ/Terra Server interpretation were collected by the Arizona and Utah teams (4%).
    • Samples collected via image (Landsat) interpretation (12%) were collected exclusively by the Colorado team, often with interpretive cues from Terraserver.
    • Samples obtained from existing databases (32%) and collected through SWReGAP fieldwork (49%) represent the collective efforts of the five mapping teams.
  10. Date of the data collection: 2000 – 2004
  11. Imagery available: Large collection of Landsat imagery also available from the USGS EarthExplorer: https://earthexplorer.usgs.gov/
  12. Other information: The field data was analyzed using a fuzzy accuracy assessment approach for the GAP Analysis project. More details are available at: