I’m very much a beginner with GIS and I’m stuck creating a least cost path.

Basically, I’m trying to highlight which river valleys would most likely be flooded in the event of a volcanic eruption producing a mudflow, which would usually follow the steepest path available. I’m using a DEM as my cost surface raster.

As I understand it, I would have to reclassify the DEM before I use the cost distance tool and then the least cost path tool. However, as I want the LCP to follow the river valley, I would need to reclassify the DEM to have many breaks (or even use the unique values button) so that the river valley is still visible and not all merged into one. Right? Or does the DEM have to be reclassified into 9 subgroups? If so, I then lose the river valley outline and I’m not sure what to do from then on. (I’ve attached some screen shots to hopefully show this).

Then I come to my next problem… If I try reclassifying the DEM so that it has 100 equal breaks and then using the cost distance tool, (with a point feature at the volcano’s vent as the source data and the reclassified DEM as the cost raster) I get the expected cost distance raster and back link raster. I then input these into the LCP tool along with another point feature that I’ve randomly placed somewhere down slope of the volcano for the destination data, I get a path output, but it’s basically a straight line and doesn’t really follow any of the river valleys like I was hoping/you would expect?

reclassify using 9 breaks reclassify using 100 breaks LCP created

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