U of M wordmark

What Do The Numbers Mean?

1. Check the heading for the date and location you are viewing.

2. Left-click on the View/Hide Statistics to show or hide the statistics table.

3. Land Cover classes identify the major land cover types of Minnesota, are compatible with existing national systems, and provide a realistic classification hierarchy for Landsat TM and ETM+ data. For more specific class descriptions, see Methods - Land Cover Classification.

The Acres of land cover classes are totaled by summing all the ~1/4-acre pixels which fall into that particular class within the unit under consideration (state, county, city, watershed, etc.). The Percent is the acres divided by Total area.

The acres and percent classified as Urban will always be greater than the Total Impervious Area and Percent Impervious Area because the urban class is not completely impervious. Urban landscapes are made up of a mix of impervious as well as permeable (0% impervious) areas such as grass and trees.

4. The Impervious Intensity ranges depict the degree of imperviousness from 0 to 100% at the pixel level -30 meters on a side or about 1/4-acre. When modeled, each pixel receives a value (24%, 67%, etc.) representing the portion of that 1/4 acre which is impervious. The values are then grouped into ranges for ease in mapping and analysis. The zero class includes the area for natural land cover types as well as the portions of the urban landscape that were modeled 0% Impervious.

Because our work is characterized as intensity ranges on a pixel-by-pixel basis, the columns of Acres and Percent represent the amount of total land falling into each of the intensity ranges as defined by pixel boundaries. The Intensity Weighted Impervious Area corrects for this by estimating the percentage of each range class (e.g., 11-25%) for the total area of the unit under consideration which is impervious.

5. Total Area of the unit under consideration is calculated using the boundaries of the GIS map coverage. These maps are used to "cookie cutter" out the pixels of satellite imagery found in a specific geographic boundary.

6. Total Impervious Area aggregates the amount of impervious area based on the percent impervious of each pixel.

7. The Percent Impervious Area is the total Impervious area divided by the Total area minus the area of water and any area with no data.