2) Cost Path analysis allows us to determine the least cost path based on slope angle (8-10% being the steepest possible angle a road can successfully be built on according to the project proposal). Using Raster data allows us to assign cost to each raster cell. By giving a high cost to steep slope values and low costs to gentle slopes, GIS can map the "cheapest" path. In this case the "cheapest" path will be the path with the most gentle slope. To make slope angle the criteria to consider in its cost analysis, we had to convert the slope values from percentages with decimals to integers. Arc GIS could not use decimal figures in its Cost-Path analysis. Thus, by going through Spatial Analyst tools > Math > Int, the values can be changed into appropriate integers.
Following this, we added the "cost" field to the attributes table of our Slope_percent layer.
DEM layer
Slope Layer
Satellite view of Area
4) Fortunately the least cost path analysis does not need to take into consideration any environmental factors as the sensitivity index layer from the Natural Resources department showed no sensitive areas in the region. Also, none of the land was privately owned allowing the analysis to forgo any monetary weighting on the land. Also, the cost analysis did not take into consideration the actual cost of building the road. As such, the length of the road was not a cost that needed to be weighed in the analysis.
3) After receiving the coordinates for the entry point of the road and the Parking lot from the project proponents we can use the distance tool to determine both Cost path and Cost distance for the access road. A second option for establishing the location of the Parking lot is to use a multi-criteria analysis tool to establish an optimum location By giving Low-slope angles, an approximate elevation of 1800 feet and a significant surface area for 30 cars high ratings Arc GIS can determine the best end point for the road.
1) The first step in this project was obtaining our data.
We retrieved environmental sensitivity, Land cover, Trail, land ownership and orthophoto data for the subject area from Alaska Department of Natural Resources online data clearinghouse.
After which, an Alaska Albers Equal Area Conic projection was used to create our own base map.
Using the Slope tool under Spatial Analysis Tools, a DEM of slope angles was projected a screen shot of which can be seen below.
The JSC sent us, along with the proposal, two maps which were hand drawn. We were able to compare our final product with the preliminary maps they had drawn.
DEM with Road
Slope layer with road
To assign friction values to slope we looked at the fact that 8 to 10% slope was the maximum allowed for a road to be safe and functional. Thus slopes with an angle of 0 to 3% were given a cost of 1, 4% a cost of 10, 5% a cost of 25 (etc). Slopes with an angle of 8 were given a cost of 100 and everything higher than 8 was given a cost of 200.
5) Thus, once we had our friction values set we were able to used them to create a friction surface layer through:
Spatial Analyst Tools > Distance > Cost Distance.
With that we could use -Spatial Analyst Tools > Distance > Cost Path, to determine the least-cost path between the nearest road and the proposed parking lot