Swan Valley, Montana Roads History: a Mapping Project

For the last year and a half, Wildlands CPR and Northwest Connections have been working together to expand road restoration in the Swan Valley of Montana. As part of this project, we worked with American Wildlands’ geographic information systems (GIS) lab (www.wildlands.org) to create a visual history of road development in the Swan Valley. This shows the progressive increase in road mileage over the last 100 years, providing a graphic picture of the current situation and how different it is from the past. The Swan Valley acts as a grizzly bear linkage zone between the Swan Mountains to the east and the Mission Mountains to the west, making the impacts of road development even more significant. Below is an explanation of the technique used to develop this map, since progressive maps like this are such excellent tools for outreach to local residents and agency personnel.

Methodology

Northwest Connections collected historic and current paper maps from the U.S. Forest Service and Plum Creek Timber Company, while American Wildlands’ GIS lab drew from other sources including digital orthographic photos and digital National Agriculture Imagery Program (NAIP) images. American Wildlands scanned the paper maps (1912-1994) and digitized roads in ESRI ArcMap, a mapping software. They used digital orthographic photos and NAIP images in combination to accurately represent roads for 2005. In each image, they manually digitized the roads. Finally, they merged the resulting layers into one, ensuring that all roads were represented.

Map produced by GIS Lab at American Wildlands. Road data is based on 1912, 1948, 1965 and 1978 USFS paper maps, 1994 and 2002 Plum Creek Timber Co. paper maps, 2003 digital orthographic photos, and 2005 NAIP imagery. Road density for 1994 was corrected for missing data in the northern part of the Swan Valley.

 

American Wildlands then calculated the average road density (miles of road/square mile of land) for each of the maps and prepared a line graph to display the increase from 1912 to 2005. However, because the road maps were largely based on paper maps (the accuracy of which cannot be verified) and digital imagery (that hasn’t been ground-truthed and has built-in errors from digitizing and cloud/tree cover), the calculated road densities are only estimates. For instance, if the same technology applied to the 2005 map was applied to the 1994 map (and possibly the 1978 and 1965 maps), the maps might look different, with the sharp spike of the last 10 years actually occurring over the last 20-30 years. That said, the road density graph illustrates the significant increase in road density over the past century in the Swan Valley.

 

 

Conclusion

The project creates a ‘visual story’ of past and current road density in the Swan Valley, and is a tool for public meetings to spark dialogue on watershed restoration needs. It is by no means a final product, but will be amended as new information is collected through local residents, agency personnel and ground-truthing. Northwest Connections and Wildlands CPR have already used these maps in public meetings and planning sessions to talk about the need for watershed restoration through road removal.