LoCoH (Local Convex Hull)
Homerange Generator
for ArcGIS 9

Installation

LoCoH for ArcGIS 9 offers a number of tools to help create home range distributions using the k-NNCH method (Getz and Wilmers 2004). To install LoCoH for ArcGIS 9, copy the locoh_arcgis9.mxt ArcMap template into your ArcGIS templates folder. In a standard installation of ArcGIS9, users templates are usually found in:

C:\Documents and Settings\user_name\Application Data\ESRI\ArcMap\Templates\

where user_name is the name of the user. Alternately, you can also save the template file in the 'global' template folder, which is usually:

C:\Program Files\ArcGIS\Bin\Templates

ArcMap templates saved in the global templates folder will be available to all users, so this location is most appropriate for installation in a multi-user environment. You can also create subfolders here (e.g., C:\Program Files\ArcGIS\Bin\Templates\Wildlife), in which case a new tab with the name of the subfolder will appear in the File -- New dialog box. For more info on working with ArcMap templates, do a search under 'Templates' in the ArcGIS 9 Desktop help.

Once the locoh_arcgis9.mxt file is in the templates folder, you can start a new ArcMap document based on the template by selecting New from the File menu. ArcMap documents based on the LoCoH template will have a new toolbar available called 'LoCoH', with a button labeled 'LoCoH'. Click this button to launch the main form.

Figure 1. Main form

Data Options

First, select the layer which contains the input data. This layer must be a point layer. You can also instruct LoCoH to only process the currently selected points in the current layer by checking the applicable box.

In the next box, enter the name of a folder where files will be saved. It is recommended that you create a new folder for data as LoCoH generates numerous files.

Finally, you must specify a base name which will be used when creating new files. Note that if any files with the same names exist, they will be automatically over-written. Thus if you want to keep the results of each run, you should change the base name each time.

Batch processing with attribute queries

Users often possess a large dataset that they desire to break up into pieces for home range estimation. For example, wet season and dry season observations might be saved in the same GIS layer. LoCoH's batch processing option allows you analyze subsets of data based on attribute values such as a date or ID number.

To subset data based on attribute values, you must create a criteria file that contains a list of attribute queries (following the same syntax as attribute queries constructed in ArcGIS). LoCoH will apply these queries to the input data, and construct a unique home range for each set of results. Criteria file should follow these guidelines:

  1. The criteria file should be saved as plain text (e.g., using notepad).
  2. Blank lines will be ignored.
  3. Any line that starts with a pound (#) or apostrophe (') character will be ignored. Thus you can use these characters to insert comments or 'rem-out' individual lines without completely deleting them.
  4. Each query expression that defines a subset of the data should be saved on a separate line.
  5. Each line that defines a subset of the data should have two parts separated by a colon.

The following is an example of a criteria file.

#A comment
_Low_Nums: "FID"<150

'Another comment
_High_Nums: "FID">=150

Specifying k

k is the number of nearest neighbors LoCoH will use to construct a convex hull. There are two ways to enter the value(s) of k:

Discrete. This is the simplest method of defining k. Just enter the value of k you want! You can also enter multiple k's if you separate them with commas (i.e. "2,5,20").

Continuous. This method allows you to specify ranges of k. 'Start' is the first k, 'End' is the upper limit and 'Step' is the increments between k. (i.e. Start:2, End:10 and Step:3, will yield k's of 2,5, and 8).

Local and merged hulls

To save the local or merged collections of hulls, check the applicable boxes.

Area vs k chart

Checking this setting will tell LoCoH to generate a chart of the various k and attribute query combinations you have set plotted against the area of the resulting merged hulls. This feature is very useful, in combination with the continuous k specification feature, if one is trying to determine what k fits the data best. Ideally one wants to pick a k just before a big jump in area which is probably a result of the hulls including out-of-bound or illegal territory (i.e. a lake).

Duplicate points

Polygons cannot be constructed out of points directly on top of one another and so LoCoH for ArcGIS has two methods of handling duplicated points:

Disallow. This setting tells LoCoH to keep searching for nearest neighbors until the necessary number of unique points is found.

Displace. This setting tells LoCoH to move duplicated points a specified distance from their original location in a random direction. This helps to preserve the real density of points.

Isopleth creation

To create isopleths, check the box and set the number of intervals you desire. You can also set the colors of the isopleths and determine the algorithm to construct the breaks between intervals. There are three such algorithms:

Quantile. Tries to place the same number of local hulls in each interval.

Equal Interval. Tries to create an equal distance between the local hull with the highest density and the local hull with the lowest density in each interval.

Natural Breaks. Uses fancy mathemagical techniques (aka Jenk's method) to minimize variance within an interval and maximize it between intervals.

Miscellaneous Options

Log Files. LoCoH creates a log file in the same directory as the data each time it is run.

Defaults. LoCoH has a lot of settings and if you are working with more than one data set it can be a real pain to switch between them. Fortunately, LoCoH has a "Manage Defaults" button that allows you to save and load collections of settings.

Copyright and License

LoCoH is copyright of the University of California. Use and distribution of LoCoH is allowed under the provisions of the GNU General Public License.

Development of LoCoH was made possible by support from the National Science Foundation (NSF/NIH EID Grant DEB-0090323).

Feedback

LoCoH is a work in progress, and we depend on the user community to provide feedback and let us know how to improve it. Please send all comments, suggestions, and reports of bugs to Andy Lyons at alyons@nature.berkeley.edu or Wayne Getz at getz@nature.berkeley.edu. When reporting a bug or error message, please provide as much background information as possible, and if possible a copy of the data that created the error. LoCoH for ArcGIS was programmed by Scott Roe-Fortmann.

References

Getz, W. and C. Wilmers. 2004. A local nearest-neighbor convex-hull construction of home ranges and utilization distributions. Ecography 27: 489-505. View PDF (1.13 Mb).