Urban Impervious Command
The Urban Impervious command of CivilGEO software allows the user to display global or regional (United States and Europe only) urban impervious surface data directly on the Map View. This command is a valuable resource for users who need to assess the degree of imperviousness across an urban study area, which is a key factor in determining runoff volumes, peak flows, and overall flood risk.
An impervious surface is any hard surface that prevents or significantly reduces water infiltration into the soil. Common impervious surfaces include rooftops, walkways, patios, driveways, parking lots, storage areas, concrete and asphalt paving, and gravel roads.
In urban watersheds, the cumulative extent and density of impervious surfaces has a direct impact on the rainfall-runoff relationship. As impervious cover increases, more precipitation is converted to surface runoff rather than infiltrating into the soil. This can increase runoff volumes and peak flow rates, reduce groundwater recharge, and degrade downstream water quality.
Impervious surface area data are useful for a wide range of engineering and planning applications, including:
- Calibrating and validating stormwater and hydrologic models.
- Estimating composite curve numbers and impervious fractions for subbasins.
- Assessing non-point source pollutant loads in urban watersheds.
- Supporting watershed-scale water quality studies.
- Evaluating the cumulative effects of urban development on flood risk.
- Identifying areas with high imperviousness that may benefit from green infrastructure or low impact development (LID) practices.
Note that a coordinate reference system (CRS) should be assigned to the project before running the Urban Impervious command. Otherwise, the software will display the informational dialog box below.
To learn more about the coordinate reference system (CRS), refer to this article in our knowledge base.
Displaying Urban Impervious Surfaces for Different Regions
To display the urban impervious data on the Map View, select the Urban Impervious dropdown menu from the Map Data ribbon menu.
The following countries are listed under the Urban Impervious dropdown menu:
| Country | Description |
|---|---|
| USA | Displays the urban impervious surfaces as a percentage of developed surface over every 30-meter pixel in the United States using the National Land Cover Database (NLCD) published in 2024. |
| Europe | Displays the data for urban impervious surfaces for the period 2018 (including data from 2017-2019) for the EEA-39 area, produced by European Environment Agency (EEA) in the frame of EU Copernicus programme. |
| Global | Displays the Global Man-Made Impervious Surface (GMIS) Dataset from Landsat and consists of global estimates of fractional impervious cover derived from the Global Land Survey (GLS) Landsat dataset for the target year 2010. |
Clicking on any of the desired countries listed above will cause the software to display the Urban Impervious dialog box, as shown below.
The Layer name entry field allows the user to define the name of a new impervious layer to be created and displayed in the Map Data Layers panel. The software sets “NLCD Impervious 2024” as the default layer name, which is editable.
The Urban impervious data source dropdown combo box allows the user to select which impervious data source to utilize for the newly created layer. By default, the software selects the latest available impervious data. The following options are available in the dropdown combo box:
- NLCD Impervious 2024
- NLCD Impervious 2021
- NLCD Impervious 2019
- NLCD Impervious 2016
- NLCD Impervious 2013
- NLCD Impervious 2011
- NLCD Impervious 2008
- NLCD Impervious 2006
- NLCD Impervious 2004
- NLCD Impervious 2001
If the “Overwrite existing data” checkbox option is checked, then the new urban impervious data selected in the Urban impervious data source dropdown combo box will overwrite the existing urban impervious data (if one exists). This is useful when updating the project to use a more recent Impervious dataset without creating a duplicate layer.
Note that for countries other than the USA, the Urban impervious data source dropdown combo box and Overwrite existing data checkbox options are not available.
Adding Urban Impervious Layer on the Map View
Once the layer name and data source have been defined, click the [OK] button to display the impervious surface data for the selected region on the Map View.
In the Map Data Layers panel, the software will provide a data legend for each impervious surface layer that lists the impervious surface percentage ranges and their corresponding color classifications included within that layer. The user can expand the layer to view the data legend, as shown below.
