Applications in GIS - Mod 2
This week's assignment was on the Natural Hazard called Lahars. Lahars refers to a rapidly flowing mixture of rock debris and water that originates on the slopes of a volcano. They pose a great hazard because more people live downstream in lahar-prone river valleys than live on the volcano's flanks and they can flow from a few meters per second to several tens of meters per second and vary in size from a few meters to hundreds of meters wide and several centimeters deep to tens of meters. Lahars are also referred to as volcanic mud-flows or debris flows.
Our assignment was to identify potential inundations zones for the Mt. Hood, Oregon area. Mt. Hood, the highest peak in Oregon, is a volcano. We started by creating a shapefile for the peak of Mt. Hood using the Add Point tool then converted that point to a feature. We then added two digital elevations rasters to run our analysis on.
Before we could do much with those images we needed to combine them into one using the Data Management tool Mosaic to New Raster. By combining these two rasters into one we were able to run the analysis on the entire area just once and without worrying about differences in symbology between to the two images.
With our rasters combined we were then able to run a series of Spatial Analyst Hydrology tools to determent the likely flow of lahars from Mt. Hood. We started with the Fill tool to be sure our stream would flow rather than pool, then the Flow Direction tool to determine the direction of flow based on the lowest relative elevation of the surrounding raster cells. With the flow direction we are then able to run the Flow Accumulation tool to determine just how much flow we have, creating a stream network, or steam raster.
Because our raster image was a floating point raster, representing a continuous surface, we needed to convert it to integer so we could run further analysis on it. We did this using the Math too Int. We were then able to access the attribute table to determine the value of 1% the total number of pixels in the raster. With this information we were able to run the Conditional tool Con. This tool defined the threshold of flow accumulation to determine what flow actually qualified as a stream. From this we were able to create a polyline feature of our final steam using the Stream to Feature tool. Once we knew where a stream was we were able to determine what population was at risk, in what cities and what schools by running queries on what fell within a 1/2 mile buffer zone from the stream.
This was a very interesting assignment and I really enjoyed it until I got to the labeling portion. I think my biggest lesson learned was that I have to spend a bit more time delving into the mechanics of labeling and get a better handle on that. I lost a lot of time trying to appropriately place my text because I didn't know how to stop it from shifting every time I zoomed in or out. Fortunately I got some leads on how to deal with that through the discussion boards so I now have the starting point I had been unable to find on my own to start an investigation. Had it not been for the labeling issue I would have finished this assignment in a quarter of the time. Hopefully this will be the last assignment I have to deal with that frustration.
Our assignment was to identify potential inundations zones for the Mt. Hood, Oregon area. Mt. Hood, the highest peak in Oregon, is a volcano. We started by creating a shapefile for the peak of Mt. Hood using the Add Point tool then converted that point to a feature. We then added two digital elevations rasters to run our analysis on.
Before we could do much with those images we needed to combine them into one using the Data Management tool Mosaic to New Raster. By combining these two rasters into one we were able to run the analysis on the entire area just once and without worrying about differences in symbology between to the two images.
With our rasters combined we were then able to run a series of Spatial Analyst Hydrology tools to determent the likely flow of lahars from Mt. Hood. We started with the Fill tool to be sure our stream would flow rather than pool, then the Flow Direction tool to determine the direction of flow based on the lowest relative elevation of the surrounding raster cells. With the flow direction we are then able to run the Flow Accumulation tool to determine just how much flow we have, creating a stream network, or steam raster.
Because our raster image was a floating point raster, representing a continuous surface, we needed to convert it to integer so we could run further analysis on it. We did this using the Math too Int. We were then able to access the attribute table to determine the value of 1% the total number of pixels in the raster. With this information we were able to run the Conditional tool Con. This tool defined the threshold of flow accumulation to determine what flow actually qualified as a stream. From this we were able to create a polyline feature of our final steam using the Stream to Feature tool. Once we knew where a stream was we were able to determine what population was at risk, in what cities and what schools by running queries on what fell within a 1/2 mile buffer zone from the stream.
This was a very interesting assignment and I really enjoyed it until I got to the labeling portion. I think my biggest lesson learned was that I have to spend a bit more time delving into the mechanics of labeling and get a better handle on that. I lost a lot of time trying to appropriately place my text because I didn't know how to stop it from shifting every time I zoomed in or out. Fortunately I got some leads on how to deal with that through the discussion boards so I now have the starting point I had been unable to find on my own to start an investigation. Had it not been for the labeling issue I would have finished this assignment in a quarter of the time. Hopefully this will be the last assignment I have to deal with that frustration.
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