METHODOLOGY

Methods for "Wildlife on the Road"

These four maps show Wildlife-Vehicle Conflicts (WVC), Traffic Counts, Roadkill (carcasses), and Roadkill density. Data for roadkill was from the California Roadkill Observation System.

For all of these maps, all highways except those in Southern California were taken out with the geoprocessing clip tool.
The WVC map was created by overlaying the points of WVC on the map of Southern California counties.
The traffic counts map is a chloropeth map. The darker the point, the more traffic counts there are on that road.
The maps with roadkill (carcasses) was also created by overlaying the points of carcasses on the map of Southern California counties.
The map of roadkill density was created by using the kernel density tool.

Methods for "Potential Overpasses"

The three areas on the maps were selected based on the Roadkill Density Map under the page, "Wildlife on the Road." The areas in Ventura County, San Diego County and near Orange County had the highest density of roadkill. Due to these high densities, only these three areas were analyzed.

Landcover and digital elevation models (DEM) were downloaded for each area of interest.
A one mile buffer was used around all the roads
With this buffer, extraction by mask was used for the landcover raster data and the DEM. This way, only raster data in the one mile buffer were analyzed
Slope of the DEM was calculated with degrees
A scoring system that ranged from points 1 to 5 was created for the landcover and slope layers
- Slope was reclassified with a scoring system. A degree higher than 45° was considered costly (1 point) and a degree lower than 45° was considered less costly (2 or more points).
- Landcover was also reclassified. More vegetation got a higher score while urbanized areas got a lower score
Map algebra was used to add the scores together and to singled out areas with a score of 7 or higher.
Those that scored 7, 8, 9, and 10 were included on the maps and showed which areas along the highway were most suitable for wildlife overpasses.

On this overpass for Liberty Canyon Wildlife Crossing in California, the slope is flat and not steep. Because of this, I determined that a smaller slope was better and least costly for a wildlife overpass to be built. This was incorporated into my maps. Source

Methods for "Endangered Mammals"

Distributions of the Bighorn sheep and San Bernardino kangaroo rat were taken from the Environmental Conservation Online System (ECOS) of U.S. Fish and Wildlife Service.

Each species distribution was placed on top of the counties they were located in
Roads were also placed over the layer
Geoprocessing tools were used to highlight the roads that intersected with the species distirbutions
Each road that intersected with the species distribution was labelled
Data Frames were created to give a closer view to each intersecting roads

Possible Data Errors

The California Roadkill Observation System data was based on observations from volunteers (professional biologists) and the median accuracy is approximately 13 meters (Waetjen and Shilling, 2017). However, volunteers may be more abundant and consistent in data collection in some areas and some may not be.

Overall the observations and volunteers on wildlife crossing site states:

Total Number of Roadkill Observations: 56487
Total Number of Registered Observers: 1400
Total Number of Unique Species Observed: 425

The complete list of data sources is located in the "Sources" page.