Landscape Analysis

One of the most common uses of landcover data at DEP is to analyze the characteristics of an area, typically a watershed, for its landcover and/or imperviousness.  A tool has been specifically developed to assist in this.

You must have the Spatial Analyst extension enabled for this tool to work.

You can find this tool in the DEP Custom Toolbox, under Analysis Tools:



This tool will create a table which provides the results of the analysis you choose.  The output table MUST be in a geodatabase.  Double-click the tool to bring it up.  The tool can compute the following 3 analyses for every analysis area, any combination can be chosen:

MELCD 2004 summaries:  Summarizes landcover classes into groups
MELCD 2004 classes:  Will give a computation of the actual area of each landcover class
MELCD 2004 imperviousness:  Provides a percent imperviousness computation

The area to be analyzed can include:

Polygons - each polygon in a data layer is analyzed separately.  A unique ID field (must be numeric) is used to relate the output table back to the polygons.  If multiple polygons contain the same unique ID, their results will be combined.  If the layer is in ArcMap, and features are selected, only the selected set will be analyzed.  Otherwise, the entire layer will be analyzed.

Hydro buffer - this choice has to be enabled in combination with at least one of the other analysis areas.  It subsets the analysis area to be a user-defined buffer around lakes, ponds, streams, and rivers.  For example, if you analyze by watershed polygons, and then use this option with a 100-foot buffer, the resulting area analyzed would be only the area within each watershed that is within 100 feet of a pond, lake, stream, or river.  Wetlands are not included in the buffer.

Circular buffers - this works the same as polygons, but the polygon used for analysis is a buffer around a point layer.  This is intended to allow analysis around sample points, or to limit watersheds to a certain distance from a sample point.

Note: You can choose either the polygon analysis, or the circular buffer analysis, or both.  If you choose both, then the resulting analysis area is the intersection of the polygon and the sample point buffer.  Also, if both are chosen, then they must have matching unique IDs so the script knows which point(s) go with which polygon(s).  If a point does not have a matching point, the script will bail out.  The hydro buffer cannot be run on its own (because doing so would attempt to buffer and analyze all the water bodies in Maine, which would take weeks to run).

Non-DEP users can download the toolbox and script for use at their own site.  The script will require some recoding to point to the correct datasets.