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Instructions for the ‘Accessible Habitat Tool’.
Description: The Accessible Habitat tool (versions 9.1 and 9.2) creates polygon
shapefiles containing only areas that can be reached from a particular site (polygon or
shapefile) without crossing a road or other linear feature (accessible habitat). It also
gives the land cover type within the accessible area. The AccessibleHabitat toolboxes can
be installed on ArcGIS 9.x and runs through a Windows interface; no knowledge of the
Python language is required for its use.
Fig. 1. Hypothetical landscapes illustrating accessible habitat. In A, all habitat (dark grey)
is accessible by some species from a focal sampling point (small black circle) without
crossing a road (thick black line). In B, C and D accessible habitat (dark grey) is less than
total habitat (light grey + dark grey). Distance to the nearest road is the same in
landscapes B, C and D, but accessible habitat is lower in landscapes C and D. Road
density is higher in landscape D than in landscape C but accessible habitat remains the
same in both landscapes.
More information on the accessible habitat concept can be found in the accessible habitat
paper (.pdf included in .zip file).
Citation: Please cite the following paper if you use the accessible habitat tool in your
work: ‘Accessible habitat: an improved measure of the effects of habitat loss and roads
on wildlife populations’ Felix Eigenbrod, Stephen J. Hecnar, and Lenore Fahrig.
Landscape Ecology (2008) Landscape Ecology 23 : 159-168. (.pdf included in .zip file).
The official version of this paper is available at www.springerlink.com.
Disclaimer: While all efforts have been made to ensure the accuracy and stability of this
tool, it is available WITHOUT ANY WARRANTY OF ANY KIND. The user must take
all responsibility for any errors and losses that occur as a result of using this tool.
Created by: Felix Eigenbrod. Many thanks to Dan Patterson (Department of Geography,
Carleton University) and SM Jones (Eagle technology Group Ltd) for providing large
chunks of the code used in writing the Python script.
Please email the author: [email protected] if you have any questions or to
report any bugs.
Software requirements:
Windows XP:
For Accessible Habitat Tool 9.1:
ArcGIS 9.0 or ArcGIS 9.1 with an ArcView license or higher.
Python 2.1: This is freely available on the web, and on the ArcGIS 9.0 and ArcGIS 9.1
installation disks. Note: Installing newer versions of Python will probably lead to
incompatibility issues. Also note that installing Python at the same time as ArcGIS (it is
part of the installation process) will probably lead to the smoothest interface between the
two programs.
For Accessible Habitat Tool 9.2:
ArcGIS 9.2 (possibly 9.3 or newer) with an ArcView license or higher.
Python 2.4.1 (This ships with ArcGIS 9.2 and should be automatically installed with
ArcGIS 9.2). All earlier versions of Python should be uninstalled from the computer.
Hardware requirements: Same as for ArcGIS 9.x
Required Files (included in zip file):
For use with ArcGIS 9.0 or ArcGIS 9.1
-AcessibleHabitat9.1.tbx – ArcGIS toolbox
-AccessibleHabitat9.1.py – Python 2.1 code for the accessible habitat tool
For use with ArcGIS 9.2
-AcessibleHabitat9.2.tbx – ArcGIS toolbox
-AccessibleHabitat9.2.py – Python 2.4.1 code for the accessible habitat tool
Instructions for installation:
The first step to using the accessible habitat tool is installing the correct Accessible
Habitat toolbox (9.1 or 9.2) for your version of ArcGIS. If you run into problems, please
check ESRI’s extensive documentation on installing and using a custom toolbox.
1. Extract the contents of the AccessibleHabitat.zip into a single folder.
2. Open ArcToolBox within ArcMap or ArcCatalog, if it is not already open. Right-click
on ‘ArcToolBox’ and go to 'Add a toolbox'. Navigate to the folder where you have
placed the contents of AccessibleHabitat.zip – two toolboxes named
‘AccessibleHabitatTool9.1 and AccessibleHabitatTool9.2 ’ should appear. Add 9.1 if
you’re using ArcGIS 9.0 or 9.1; add 9.2 if you’re using ArcGIS 9.2 or higher, and you'll
see the AccessibleHabitat tool will be contained within it. Right-click ArcToolbox again
and click ‘Save settings’ –‘To default’. Saving settings means that the accessible habitat
toolbox will now appear every time you open ArcToolbox.
4. Right-click on the AccessibleHabitat tool to get a pop-up menu. Choose 'properties',
and click on the 'Source' tab within "properties".
You'll see that the default source is pointing to a directory where I keep my Python
scripts, which will be of no use to you. Browse to the folder where you've put the toolbox
and click on the AccessibleHabitat9.x.py script, and then hit 'Apply'. If you’re using
ArcGIS 9.0 or ArcGIS 9.1, you’ll need the AccessibleHabitat9.1.py script; if you’re using
ArcGIS 9.2 or newer, use the AccessibleHabitat9.2.py script.
Using the Accessible habitat tool:
Required input for the Accessible Habitat Tool:
Once you have installed the ‘Accessible Habitat’ toolbox, left-click on the ‘Accessible
Habitat Tool 9.1 (or 9.2)’ within the toolbox to use the tool. You will see the following:
Input is required for each of the six fields for the tool to run.
IMPORTANT NOTE: All input files MUST be in the same projection to get meaningful
results. I use the UTM co-ordinate system in my analyses with meters as the unit. The
tool should run using any mapping unit (e.g. cm, miles) and co-ordinate system, but this
has not been tested. Also note that the geographic co-ordinate system (lat/long) is
inappropriate for geospatial analysis.
1. Point/polygon shapefile with all sites (site file): A shapefile with all your sites
(points or polygons) (site file). For example, you might have a point shapefile
names sites.shp, with 30 points at which you conducted anuran call surveys.
2. ID field in site file. Must contain string or integer values. Your site file must
have a field giving the names of individual sites within the site file. For example,
your file sites.shp might contain an ID field name ‘SITENAME’ which gives the
names of your sites; e.g BigPond1, Bluwater2, Mud Lake, etc.
3. Polygon file with road layer. This is the file that is used to delineate accessible
habitat. It will usually be based on a line shapefile (e.g. a road layer) which has
only the types of linear barriers that you want to use to delineate accessible
habitat. For example, you might have created a polygon file named
‘Freeways.shp’, which gives polygons based just on freeways in the region where
study sites (site.shp) are located if you only want to use freeways to delineate
accessible habitat:
4. Polygon land cover file. This shapefile is used to define habitat in your study
region. For example, if for the species you are interested in forests are habitat,
then this file should just show forested areas, so you can then calculate the
accessible forest near each of your study sites:
5. Folder for Accessible Habitat files. All output shapefiles will go into this folder.
If you have a large number of sites, and want to calculate accessible habitat at a
number of distances from your sites, this can be a substantial number of
shapefiles. In our example, sites.shp has 30 points. If we calculate accessible
habitat within 100 and 200 m of each of these sites, we will get 60 output
shapefiles, each labelled by the ID field and the radius distance.
6. Buffer distance(s). A list of distances of radii from the sites you're interested in
(i.e. you may want 200 m, 400 m and 600 m radius buffers of your sites).
IMPORTANT NOTE: If your input sites are polygons (e.g. focal patches of
forest), the area of these focal patches will not be included in the calculation of
accessible habitat. In addition, buffer distances will be calculated from the edge of
the polygon (NOT the centroid), so if your input focal patches differ in size, then
the area of the buffers will differ in size. It is thus advisable to calculate
percentage of accessible habitat rather than absolute values when using sites that
are polygons. If your sites are points, then all buffers will be the same size, as a
point has no area.
Output from using the Accessible Habitat Tool
Polygon shapefiles giving accessible habitat for each site at each buffer distance will be
written to the output folder. Each shapefile gives the amount of land (and land cover
type) that can be reached from a particular site without crossing a barrier within in a
particular distance of the site (the buffer distance). Thus if you have 30 sites in your input
shapefile and want to look at the amount of accessible habitat within 200 m and 400 m
buffers you'll get 60 output shapefiles. These output shapefiles will be labelled using
both the ID field and the buffer distance. For example, if you have site name ‘Mud Lake’,
you will get shapefiles named “Access_Hab_200_Mud Lake.shp” and
“Access_Hab_400_Mud Lake.shp”.
Errata
The Accessible Habitat tool may crash due to a lack of memory if a large number of sites
and/or buffer distances are run at one time. This is due to a memory leak program which
is a known issue with ArcGIS. What constitutes a ‘large’ number of sites will depend on
available RAM, the size of the buffers, the complexity of the land cover shapefile, and
the idiosyncratic behaviour of ArcGIS.