Lab 11: Terrain AnalysesGIS Fundamentals Lab11: Terrain Analysis 1 Lab 11: Terrain Analyses What You’ll Learn: Basic terrain analysis functions, including watershed, viewshed, and profile processing. There is a mix of old and new functions used in this lab. We’ll explain the new, but you are expected to review old labs if needed. You should read chapter 11 in the GIS Fundamentals textbook before performing this lab. Data are located in the \L11 subdirectory, all in NAD83 UTM zone 15 coordinates, meters, including driftless, a raster elevation grid, 3m cell size, Z units in meters, and driftless30, a raster elevation grid, 30m cell size, Z units in meters. A shape file called viewspot.shp is also used in this lab. What You’ll Produce: Various hydrologic surfaces, a watershed map, a viewshed map, and profiles. Background Elevation data, also known as terrain data, are import for many kinds of analysis, and are available in many forms, from many sources and resolutions. In the U.S. there have long been available nearly nationwide data at 30 m resolution. Since the early 2000’s these have largely been replaced by 10 m resolution DEMs, and now many parts of the country are developing higher resolution DEMs, and 1 to 3 meters, based on LiDAR data collections. Although the most common use of DEMs is as shaded relief background for maps, we often are interested in working with terrain data – calculating slopes, aspects, steepness or slope along profiles, viewsheds, as well as watershed and other hydrologic functions. The readings and lectures describe some of these applications, and this set of exercises introduces them. We will complete two projects here, using the same basic data. The first project has two parts, first comparing raster data sets of 2 vintages, a 30 meter data set from the USGS and produced in the late 1980s, and a 3 meter data set from LiDAR data collected about 2006. We then use the LiDAR DEM to explore profile and viewshed tools. Our second project focuses on watershed processing, using the ArcGIS Hydrology tools.GIS Fundamentals Lab11: Terrain Analysis 2 Project 1: Raster Surfaces, Profiles, and Viewsheds Start ArcGIS - ArcMAP Create a new map project, add the raster driftless to the view, and inspect it. Use the cursor and the layer Properties –Source tab. What is the cell resolution? What are the highest and lowest elevation values? Now add the raster driftless30, and inspect it for resolution, cell size, and values. Use the ArcToolboxSpatial Analyst ToolsMap AlgebraRaster Calculator to subtract driftless from driftless30. Inspect the range of differences in elevation, and note where they largest differences tend to occur. Unclutter the view by removing the driftless30 DEM and the difference layers from the map. Derive the hillshade for driftless by ArcToolboxSpatial Analyst ToolsSurface Analysis – Hillshade, specify 25 for the Altitude and model shadows. Name the output file something like hs_drift. Make the hillshade semi-transparent (Layer Properties Display, then set the transparency to something like 50%, see Lab 6). You should get a display that looks approximately like the graphic to the right. Turn on the 3-D Analyst extension, CustomizeExtensions, then check 3D Analyst, then CustomizeToolbars and also check 3D Analyst. (Video: Add profile) This displays a new set of off tools, including the icons below. We’ll now explore the Line of Site and Profile View options. First, add the viewspot shapefile. This shapefile displays a single point, in the bottom left portion of the driftless DEM; it isn’t needed for a profile, but we will use it for our next operation.GIS Fundamentals Lab11: Terrain Analysis 3 Activate the Line of Site tool ( ). This will open a Line of site window (see right). Enter 2 for the observer offset (height, in meters here), and leave a value of 0 for the target offset (height). Now, left-click approximately on the point in the viewspot shapefile, found in the southwest quadrant of the driftless DEM. Move the cursor up to somewhere near the top of the DEM, and left-click again. (Hint: if you make a mistake push Delete and start over) This should display a profile line over the DEM, similar to the one shown on the right. The profile line is a graphic element placed on the data and layout views. The default settings show areas not visible along the line colored in red, and areas visible colored in green. Left-clicking on the Profile Graph tool displays the corresponding profile graph, as shown below. The profile graph shows the same profile line trajectory, but in a side view, and uses the same green/red coloring scheme. It shows the elevations on the vertical axis, and the horizontal distance on the horizontal axis.GIS Fundamentals Lab11: Terrain Analysis 4 Note that right-clicking on the profile graph displays a menu, and with the Properties option (see below) you may change the graph appearance, titles, and other properties. You may add a graphic of the plot to your layout by right clicking on the Profile Graph, and left-clicking Add to Layout (see below), or you may copy as a graphic or export to one of several image formats. After adding the graph to your layout, double check that it has appeared in the layout view. While the profile tool and graph show visibility along a specific path, we may wish to know all areas visible from a point, rather than just along a profile line. We could create a data layer that would show areas that are visible and hidden. We may do this with a viewshed function. To access this function via use: ArcToolbox Spatial Analyst Tools Surface Viewshed This should display the menu at right, in which you should specify driftless as the input raster, viewspot as the input point feature, an output raster name, and a Z factor of 1. This will then create a raster with all raster cells for the area covered by driftless categorized as either visible or not visible from the viewspot point. Make the non-visible cells transparent (assign no color to the symbols), and assign some appropriate color to the visible cells. Switch to the layout view, and add the usual title, name, north arrow, legend, and scalebar elements, similar to the graphic at right. Save your project, and export a .pdf of this layout, similar to that shown left.GIS Fundamentals Lab11: Terrain Analysis 5