Chapter 5 Create Backgound Data

This chapter will describe the process used to calculate background data for input to the Maxent model. Background point data are used to define the habitat available to mussels within the study area.

HREP Mussel Modeling Workflow, Calculate Background Step.

Figure 5.1: HREP Mussel Modeling Workflow, Calculate Background Step.

5.1 Create Background Data

Create a background to constrain points to aquatic areas (more data resolution) and reduce Maxent run times.

  • Use the Create Random Points (Data Management) tool to create a background restricted to aquatic areas:

    • Output location: \\mvrdfs\EGIS\Work\EMP\HREP_Projects\SteamboatSlough\Mussels\SteamboatMusselModel\Data\SB_Mussels.gdb\
    • Output feature class: background
    • Constraining feature class:aquatic_areas_20m
    • Number of points: 10000
    • Minimum allowed distance: 25m
    • Leave all others as defaults
    • Click OK to run the tool
  • In the background feature class, add 3 fields, one named species, Type = Text and Length=20; one named longitude, Type = Double; and one named latitude, Type = Double.
  • For the species field use the Field Calculator tool to set the value of the field to species = “background”.

  • Use the Calculate Geometry tool to populate the longitude and latitude fields, ensuring that the coordinate system is set to NAD 1983 2011 US Feet and StatePlane Illinois West FIPS 1202 and the units are set to US feet.

5.2 Export to Maxent “SWD” Format

The purpose of this step is to assign the environmental predictor values (AdH hydraulic variables and optionally the wind/wave variables) to each of the background points. The Maxent documentation refers to this format as the “Samples With Data” (SWD) format because it contains the samples (i.e., sample identifier, latitude, longitude) with the environmental predictor variables (e.g., q5_velocity, q5_depth, q5_slope, etc.).

  • Ensure all environmental predictor layers have the same spatial reference as the background feature class.

  • Use the Extract Multi Values to Points (spatial analyst) tool to write new values (velocity, depth, slope, and ss) onto the background feature class.

    • Input point features: \\mvrdfs\EGIS\Work\EMP\HREP_Projects\SteamboatSlough\Mussels\SteamboatMusselModel\Data\SB_Mussels.gdb\background
    • Input rasters: q5_velocity, q5_depth, q5_ss, q5_froude, q5_reynolds, q5_slope, q95_velocity, q95_depth, q95_ss, q95_froude, q95_reynolds, q95_slope.

  • Export the background feature class attribute table as a .csv file. Ensure the ObjectID field is deleted using Excel prior to use in Maxent.