Deliver your responses (described below) into the appropriate Dropbox
Value: 10% of the course grade
Penalty for late delivery: This assignment will be penalized two points up to four days late. No points will be given for submissions more than four days late.
A considerable amount of environmental analysis depends upon raster data. The variety of continuous phenomena that define our world, such as elevation, land cover, and precipitation, are captured and represented in GIS-friendly raster data using a combination of remote sensing technologies and computational modeling to derive the finished products. Of course, a defining feature of any raster is the shape and size of the pixels. Choosing one’s scale of analysis – which, when working with raster data means choosing the resolution (cell size) of the rasters to be studied – is an important consideration for any environmental study.
In this project, you will study a portion of land in the San Fernando Valley section of Los Angeles using raster data at three different scales: 30m, 10m, and 1m. The study area is a bounding rectangle slightly larger than the Browns Canyon Wash, a canyon within the Santa Susana Mountains. Precipitation that falls in the wash drains to form Browns Canyon Creek, a tributary of the Los Angeles River. Browns Canyon Wash is thus a watershed, also called a catchment or basin, which is itself a sub-watershed of the Los Angeles River watershed.
Your first task is to create rasters of hillshade, slope, and aspect of the study area using the digital elevation model (DEM) data and visually compare the results. Your second task is to assess the hydrology of the area by studying how water flows and accumulates over the terrain. Your analysis will yield an outline of the estimated watershed boundary of the Browns Canyon Wash at each resolution. You will compare the boundary derived from the three different DEM scales with each other and with the official USGS watershed boundary shapefile. The workflow has already been completed for the 10m DEM; you will run the workflows for the 1m and 30m DEMs and compare the results for all three and the USGS boundary.
Raster data at different scales serve different purposes. Small cell size, such as 1m, provides highly precise information. This level of precision is useful for some but not all studies (see Avelino, et al. 2016, cited below). Working with such precise data means working with relatively larger file sizes and the larger amounts of resources – data storage space, bandwidth (for cloud computing), and time – required. Data with larger cell sizes provide less precise results but can be better aligned to certain projects’ goals; and it can be much easier to work with. As with all things spatial, you will need to match the data you use with the goal and parameters of any particular project.
Note: While we encourage discussion of challenges encountered and troubleshooting, each student is expected to undertake their own technical work, provide screen captures/map of their own outputs, and complete their own written report
• Analyze land surface parameters at different scales.
• Evaluate different methodological choices for terrain and hydrological analyses
• Synthesize methodological considerations and geoprocessing outputs via a high-quality written report
1. Read / Watch the following. URLs are provided in Sources and Resources, below.
• Bolstad, GIS Fundamentals textbook, Ch. 11 Terrain Analysis.
• Avelino, A.F.T., Baylis, K., Honey-Rosés, J. 2016. Goldilocks and the Raster Grid: Selecting Scale when Evaluating Conservation Programs. PLoS ONE 11(12): e0167945.
This article provides an interesting case study of differing results when using different scales of rasters. Focus on sections 1, 2, and 5. Skim sections 3 and 4.
• Law and Amy, Getting to Know ArcGIS Pro workbook, Exercise 9B: Derive new surfaces and Exercise 10C: Create a page layout.
Review these workflows for information but you are not required to work through the assignment or submit any deliverables from this.
• Esri help pages:
o An overview of the Hydrology toolset (and the associated help pages on the various tools in the toolset as well as the Hydrology toolset concepts pages).
o An overview of the Surface toolset (and the associated help pages on the various tools in the toolset as well as the Surface toolset concepts pages).
• Esri videos:
o Leveraging ArcGIS Elevation Analysis Services.
2. Complete the following Esri web course.
• Terrain Analysis Using ArcGIS Pro. This covers similar ground as Exercise 9B of the GTKAGPro workbook (no pun intended).
3. Copy Project4.zip from the H: drive to your G: drive. Extract the contents. The Project4 folder contains the following data.
Within the USGS_NED_1_n35w119_GridFloat folder:
• usgs_ned_1_n35w119_gridfloat.flt o “usgs” = US Geological Survey o “ned” = National Elevation Dataset
SSCI 581: Concepts for Spatial Thinking Project 4
USC Spatial Sciences Institute © 2021 3
o “1” = 1 arc-second (a measurement of length in geographic coordinate systems, equal to 1/3600 of a degree), which is ~30 meters; this refers to the pixel edge length, so this dataset is a grid of 30m by 30m cells (900m2)
o “n35w119” = the coordinates of the northwest corner of the grid o “gridfloat” = the numeric structure and data type o Source: USGS 3D Elevation Program
Within the USGS_NED_13_n35w119_GridFloat folder:
• usgs_ned_13_n35w119_gridfloat.flt o “13” = 1/3 arc-second, or ~10 meters, so this is a grid of 10m by 10m cells
(100m2) o Source: USGS 3D Elevation Program
Within the Project4.gdb:
o This is a 1m DEM (each cell is 1m by 1m (1m2)) of our study area, that has already been prepared for your use. The preparation involved acquiring a series of contiguous DEMs, running the Mosaic to Raster tool to stitch them together in one file, and running the Extract by Mask tool to limit the extent to our study area.
o Source: USGS 3D Elevation Program
• A series of rasters that are the result of the workflow described herein for the 10m DEM
o This is a polygon which demarcates our study area. You will use this to limit the size of the 30m DEM (as described above, this step has already been completed for both the 1m and 10m DEMs).
o Source: USC Spatial Sciences Institute
o This is a polygon which demarcates the boundary of the USGS-defined Browns Canyon Wash watershed. It is at the HUC-12 level in the hierarchy of watersheds. You will use this for comparison with your results.
o Source: USGS Watershed Boundary Dataset
4. Explore the project. From the Project4 folder, open the Project4.aprx. The map contains the World Imagery basemap and the rectangle that demarcates our study extent. The US Detailed Streams layer has been added to the map from the Living Atlas. You can turn this layer on and off to compare against your own streams after running the Flow Accumulation tool. In the Catalog, explore the data layers in the Project4 folder.
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