Latest Contributions by AureliusDokeianos

Hi, I'm working on a least-cost path project for part of my history dissertation, but I'm uncertain about one stage of the data preparation and I thought I might be able to find some thoughts on the issue here. I'm essentially doing what Rosenswig and Martínez Tuñón are doing in their June 2020 Journal of Archaeological Science article: creating a cost surface from elevation and hydrology data and then using Tobler's Hiking Function to come up least-cost paths and contour lines that tell me approximately how long it took to move across a certain distance on foot. My specific workflow is very close to 11.2B of the Berkeley Geospatial Archaeology course. I've run a few tests on a small area and so far things work out just fine when I'm using either a DEM or a slope generated from my DEM as the input surface raster in the path distance tool. The results are what I expect them to be. So, two questions: 1. DEM vs. slope? The results are very similar in my 75km test zone, but the analysis I'm performing will extend out to about 800 kilometres, so even small variations will add up. Is one of these methods more acceptable? 2. How do I go about creating my input surface raster? I'd like to add a layer of hydrology. I've created weighted cost rasters in the past, but Rosenswig and Martínez Tuñón had a different solution: give the water bodies slope values based on how easy they think it is to traverse. I tried reclassifying my hydrology rasters and then combining them with the slope from the DEM, but path distance does not like the resulting raster, presumably because when I used the combine tool, the results were not in degrees. Could anyone point me towards what I should be doing to make this work? ... View more

Hi all, I need to run a bunch of viewsheds that are going to take some time to compute. I'd like to set them up so that they will run sequentially overnight. I figured that the best way to do this was with ModelBuilder. Now I've never used this before, but I read some tutorials, watched ESRI's video on Youtube, and what I am trying to do is very simple. And this is the error I get when I try to run my test model. It gives me the little yellow "I'm ready to go!" shading, but then breaks immediately. I haven't even added a second process, and I'm not quite sure how, but that's a problem for later. I'm baffled. When I turn and run the exact same process through the geoprocessing tab, it works just fine. My data is not the problem here. I probably made some very elementary mistake here. Does anyone know what might be wrong? ... View more

Hi all, I'm writing here to get your thoughts on the methodology of a simple GIS project that I hope to have form a chapter in my (history) doctoral dissertation. Most of what I know about historical GIS is coming from a range of articles in the Journal of Archaeological Science and is there applied to pre-literate or pre-historical cultures, but I'm attempting to bring some of their methodology into the study of the near east in the Middle Ages. So I'm looking at a contested border zone, a sort of no-man's land. I built myself a cost surface from a DEM, hydrological features, and some ground cover data. In my area of study I have about a dozen points indicating settlements or fortresses. So I ran a series of least-cost paths, from every point to every other point. We have a historical text pertaining to this time and place which discusses the sort of low-intensity warfare that was conducted. The idea behind generating the LCPs was to provide an alternative to our poor knowledge of the roads in the area, as well as to get a sense of where else people might be moving when the roads were being watched. Ambush and tracking of raiding parties was a big part of warfare in this region. So what I'm doing is taking the polylines generated by the LCPs, turning them into rasters, and then performing viewsheds along the entire length. Rather than identifying what can be seen, I'm interested in what the viewer on these paths cannot see, ie: potential locations where one might hide ambushing forces, and how those defending might have been able to move around the landscape without being detected or intercepted. So I have a couple of questions that those with more GIS knowledge might be able to help me with. 1. Does anyone know of any similar, published work? As a GIS novice, all my methodologies are borrowed from others. 2. I have been using the line rasters to create the viewsheds, but am I correct in believing that the viewshed tool is taking vertices along the line as the points in which it makes the viewshed from? For example, in this image the green line is the original cost path, the purple is the raster line made from the cost path, and the circle un-seeable zone is probably there because it's only taking viewsheds from the two vertices rather than any points along the line? 3. If the answer to number 2 is yes, I should probably manually create a series of points along the line and then use Modelbuilder to run many viewsheds automatically? 4. Are there better tools or methods to go about doing this project? Thank you for your time. ... View more

Hi all, Sorry if this is in the wrong place for this. I've been looking online for something akin to Esri's light grey canvas base map but without the national boundary lines. My work concerns the pre-modern world, so those lines are not applicable. Is there a version out there without them, or a simple way to remove them? ... View more