Impervious Surface Analysis Tool - Help
Run Impervious Surface Analysis
Land Cover Grid | Land Cover Grid Units | Analysis Theme | Analysis Field | Coefficient Set | Output Shapefile | Theme Name | Land Cover Change Scenarios | Run Button | Quit Button
Land Cover Grid
This drop-down menu is used to select the Land Cover Grid theme that identifies the land cover classes to which impervious Coefficients will be applied. The drop-down list shows all grid themes within the current view.
Land Cover Grid Units
The Land Cover Grid Units field specifies the units (feet or meters) of the selected Land Cover Grid. Impervious surface area will be reported in acres or hectares depending on whether the input was in feet or meters, respectively. If the "Measurement Units" value is set for the view, those units will be the default units used for the Land Cover Grid Units.
Analysis Theme
The Analysis Theme is the polygon shapefile or ARC/INFO® coverage that is used to define the areas over which impervious surface estimates will be calculated. The analysis is performed either on selected polygons, or on all polygons if none are selected. The Analysis Theme drop-down menu lists only the themes from the current view that contain at least one attribute of type string or integer.
Analysis Field
The Analysis Field specifies the attribute in the Analysis Theme that defines the grouping of areas that will be assigned a unique impervious surface value. Imperviousness in all polygons having the same Analysis Field value will be combined to calculate total impervious area and percentage of impervious surface for those polygons. The Analysis Field drop-down menu only lists attributes of string or integer type within the Analysis Theme.
The Analysis Field chosen will depend upon the attribute fields within the Analysis Theme and the size of the areas to be investigated. To calculate an impervious surface value for each polygon feature within the analysis theme, select a field that uniquely identifies each polygon.
Coefficient Set
The coefficients referred to in the Coefficient Set dialog define the percentage of imperviousness for each land cover class in the Land Cover Grid. Select the Coefficient Set to be applied when estimating the impervious surface. The drop-down menu lists all coefficient sets that are currently defined. The coefficients in the set must match the type of land cover grid selected under Land Cover Grid.
The coefficients provided with the tool were developed for use with Coastal-Change Analysis Program (C-CAP) land cover data. If you are not using a C-CAP land cover grid theme, you will need to define a new coefficient set using the Change Coefficients option from the Impervious Surface Analysis Tool pull-down menu.
The imperviousness of a single land cover class may be affected by population density. Several ranges of coefficients are available to provide a means of including the effect of population density on the percentage of imperviousness within a given land class. One can choose to apply a coefficient for a single range of population (i.e., High, Medium, or Low), or to calculate the population in each area from an additional polygon data layer, if available.
Which Coefficient? allows one to force the Impervious Surface Analysis Tool to apply the same coefficient set (High, Medium, or Low) to all regions. If the Calculate option is chosen, the tool will determine which coefficient (High, Medium, or Low) to apply based on a user-defined range of population values. The range is entered using the Population Density Calculation dialog, which is displayed when the Calculate option is clicked.
Population Density Calculation
The Population Density Theme is the shapefile or arc coverage polygon theme that contains population density values. The Definition Field is the attribute field within the Population Density Theme that contains the population density data. The Definition Field must be a numeric field. Specify the values that define the cutoff values for high and low population densities. Click OK to apply this population density information.
Output Shapefile
The Output Shapefile dialog is used to specify the name of the impervious polygon shapefile that will be generated by the tool. Click Browse to navigate to the directory of your choice.
Theme Name
The Theme Name allows the user to name the impervious polygon shapefile something other than the default Output Shapefile name.
Land Cover Change Scenarios
The Land Cover Change Scenarios function allows the user to incorporate land cover changes into the generation of a new impervious surface layer.
Click the Add button to define a land cover change scenario. The first input asks the user to Change land cover classes within . . . and requires the input of a polygon theme that defines the specific area that will change. Usually this theme will be a shapefile representing a subset or a smaller, more specific area within the Analysis Theme.
The second portion of this input asks . . . theme to . . . and requires the user to select the land cover class to which the area will change. There is no limit to the number of land cover change scenarios a user can define. However, the greater the number of defined scenarios used, the longer the analytical process will take. After selecting the changed land cover, toggle on the Apply box and then hit the Run button located on the bottom of the dialog box to start the process. A scenario will not be evaluated unless the Apply box is checked.
The Delete button allows the user to delete a land cover change scenario. This function will prompt the user to enter the number of the land cover change scenario to delete. Simply enter the number, then hit OK, and the scenario will be deleted.
Run button
Click the Run button to start the analytical process to create the impervious surface coverage. After processing is complete, the view will contain a new theme representing the estimated impervious surface for each unique Analysis Field within the Analysis Theme.
Quit Button
Click the Quit button to close the impervious surface analytical tool.
View ISAT Parameters for a Theme
View ISAT Parameters for a Theme displays the file theme_name.prm, which contains a list of ISAT parameters used to generate an impervious surface layer in ISAT. Parameters include land cover grid name and units, analysis theme name and field, coefficient option choices, coefficient values, and change scenario description.
View ISAT Metadata for a Theme
View ISAT Metadata for a Theme displays metadata for a selected impervious surface layer generated by ISAT. The metadata is almost Federal Geographic Data Center (FGDC)-compliant. Users must edit the file (theme_name.met) to add bounding coordinates and datum/projection. There will be valid latitude/longitude values if the vector data within the view are geographic. Otherwise, the values represent the bounds based on the datum/projection of the vector data. The datum/projection is unknown by ISAT and will require updating by the user.
Change Coefficients
Coefficient Set | New | Import | Export | Merge | Change Coefficients Table
Coefficient Set
Select the Coefficient Set to view or edit.
New Coefficient Set
Click the New button to create and save new coefficient sets for your land cover data. Check the box labeled Model after an existing Coefficient Set, and select the Model After coefficient set on which the new coefficient set will be based. If Model after an existing Coefficient Set is not checked, an empty coefficient set is created.
Import Coefficient Set
Click the Import button to import an impervious surface coefficient set into ISAT. The file must be a comma-separated value text file (*.csv text file). This function can be used to import coefficients from a spreadsheet or text file without entering the coefficients individually into ISAT.
Export Coefficient Set
Click the Export button to export an impervious surface coefficient set to a Coefficient Text File (*.csv text file). The coefficient set can be accessed and modified in a text editor or spreadsheet.
Merge Coefficient Collections
Click the Merge button to combine two impervious surface coefficient collections. All coefficient sets from a selected coefficient XML file are merged into the user's current coefficient XML file, isprops.xml. This provides a useful way to share coefficient sets between users. Coefficient sets are stored in an XML formatted file located within the ArcView install directory, typically C:\ESRI\AV_GIS30\ARCVIEW\ETC. This XML file is read by ISAT to identify the coefficient sets listed in the Coefficient dropdown list.
Change Coefficients Table
The Coefficient Set is composed of multiple rows of Class Value, Class Name, and Coefficients. A row should be created for each unique value defined for the land cover grid. The class value represents the grid value for a land cover class and must be an integer. The class name is a text description of the land cover class. Right-click the mouse within the coefficient table to activate a pop-up menu to Add, Insert, or Delete rows. The Coefficient column shows High, Medium, and Low impervious surface coefficients for each land cover class. These levels are based on the population density of the area of interest. The coefficients represent the percentage of imperviousness for a land cover class and must be a number between 0 and 100.
The coefficient sets included with the model were derived from C-CAP data and impervious surface data in the State of Connecticut. The coefficients may need to be adjusted to apply them to other areas.