The Integrated Decision Unit (IDU) Shapefile Coverage

The Integrated Decision Unit (or IDU) shape file is a GIS coverage that contains the polygons that form the decision units for ENVISION. It must conform to ESRI’s Shape File specification. The polygon geometry can be defined by the application developer at what ever scale and with whatever geometry is appropriate for the application. If the decisions to be modeled are made at a tax lot (parcel) level, then parcels might be an appropriate IDU. If some other decision unit is appropriate, the IDU geometry should reflect that. The IDU Shape file to use for a given application of ENVISION is specified in the [layers] section of the Project file. Note that multiple layers can be specified in this section; the first is assumed to be the IDU coverage. All IDU attributes must be contained in the IDU coverage – multiple IDU coverages in a single application are not currently supported in ENVISION. It is important to emphasize that ENVISION can ONLY deal with landscape information that is represented in the IDU coverage. The IDU coverage should contain any attributes that are needed by any of the following:

  • Policy Site Attribute Query
  • Policy Outcomes
  • Plug-in Models
  • Evaluators
  • Visualizers

Most GIS tools (e.g. ArcGIS, GRASS, etc) support the creation and editing of shape files. The Envision desktop interface incorporates a number of capabilities for modifying shape files - see below for details.

Additionally, there are are a small number of attibute fields required to be present in the IDU coverage, specified as follows. These can be added in with any software capable of manipulating Shape file databases; additionally ENVISION has the ability to add these fields automatically or manually (see Data Preparation Functions for more information.)

Attribute NameData TypeDescription
LULC_A
LULC_B
LULC_C
Integer Land Use/Land Cover (LULC) classes. ENVISION employs a n-tier hierarchy of LULC classes, with up to four tiers specified. LULC_A is the top-tier class, representing the most aggregated LULC descriptors. LULC_B is a more articulated version, and LULC_C is the most articulated version of the LULC classes. This concept of an LULC hierarchy is employed to allow Site Attributes and Outcomes to be specified at various levels of generality. The specific classes used in each classification level can be defined by the application in a comma-delimited file specified in the lulcTree setting in the Project file. If only LULC_C attributes are specified in the IDU coverage, ENVISION can populate the LULC_B and LULC_A fields automatically – see Data Preparation Functions in the manual for more information. LULC_A is required at a mimimum; LULC_B and LULC_C are optional.
AREA Numeric, Single or DoubleContains the area of the IDU. This can be populated automatically by ENVISION - – see Data Preparation Functions in the manual for more information.
POLICY Integer ENVISION uses this column to store the most recent Policy ID to be applied to an IDU. It does not need to be populated by the developer; it just needs to exist in the IDU coverage.
POLICYAPPS Integer ENVISION uses this column to store the most number of policy applications made to an IDU. It does not need to be populated by the developer; it just needs to exist in the IDU coverage.
LASTD Integer ENVISION uses this column to store the year in which the last actor decision was made for this IDU. It does not need to be populated by the developer; it just needs to exist in the IDU coverage.
NEXTD Integer ENVISION uses this column to store the year in which the next actor decision is scheduled for this IDU. It does not need to be populated by the developer; it just needs to exist in the IDU coverage.
STARTLULC Integer ENVISION uses this column to "remember" the initial LULC_C value of the IDU. This columns needs to be present, but ENVISION populates it automatically.
UTILITYID Integer This is only used if Actor decision-making based on utility is enabled. In that case, an autononous processes should be defined that populates this field with the policyID of the policy that maximizes utility for the given IDU



ENVISION contains a number of built-in data preparation functions that simplify and automate certain aspects of IDU coverage development. These are listed under Data Preparation tab on ENVISIONs main menu, and are described below:
Menu OptionDescription
Merge With a Different DatabaseAllow the columns of a separate spatial database (dbf) to be merged into the IDU coverage. Individual fields to be merged can be selected. The database to be merged should have matching geometry and IDU’s.
Add Field(s) Adds a new (unpopulated) column (field) to the IDU database.
Remove Field(s)Removes column(s) (field(s)) from the IDU database.
Calculate FieldPopulates a field with a value computed from other fields.
LULC HierarchyExamines the LULC_C field and populates the LULC_B and LULC_A fields based on the current LulcTree hierarchy information.
Distance ToAllows population of “closest distance to” fields by calculating the distance from every point or the centroid of every polygon in a target layer to the points or polygon edges in a source layer. For example, the distance to a stream or business district for each IDU can be calculated and populate an approriate field, as long as a query identifying a stream or business district in some layer can be formulated.
Adjacent ToAllows population of a database field with the index of “adjacent” polygons.
Project to 3DIn conjunction with an ESRI ASCII GRID DEM file, projects the IDU to 3D and allows storage of the IDU coverage as a 3D shape file.
Populate AREA Field Populates the AREA field with an IDU’s area, computed from the IDU geometry in the units of the shape file.